This is how I see it:
At Pos. 3 Green has chosen to go wide and outside of Blue and Yellow so cannot be given Mark room.
At Pos. 3 Green is outside the zone so 18 is off in respect to her but still applies to Blue and Yellow.
At Pos. 4-5 18 is back on as the boats have yet to clear the mark.
At Pos. 5 Blue is clearing the mark and has been Mark room by Yellow so 18 is off for her but Green has not given Yellow room so is in force on them. Green breaks 18.2b 

In tight quarters, as has been described, green may not believe that they were outside the Zone therefore 18.2(c)(1) applies and yellow has no rights inside green.
The question to green, did you go outside the Zone?

Green loses her right to mark-room by leaving the zone but she has to give the other boats mark-room.
at position 5 all boats have had the mark room to which they were entitled and now 18 is off.
At 5 between yellow and green it is a RRS 15 and
 16 matter.

Bolla .. I don't think the last sentence of 18.1 comes into play here.

Because this is a gate, 18.4 does not limit Green’s course before she gybes.

At position #3, 

Between position #4 - #5 ...

More facts would be needed, but it appears that Green being faster than Yellow, changes course toward while overtaking Yellow, but does not give Yellow opportunity to keep-clear.

DSQ Green for breaking 16.1 (or maybe 15) and 14.

Let's change it up slightly .... 

Assume that this is not a gate, but a single rounding-mark-#1 and that Green and Blue are still overlapped at position #2-1/2 just before Green leaves the zone.

Does Green break 18.4 vs Blue at position #2-1/2?

Does Green break 18.4 vs Yellow at position #2+ assuming Green passes clear ahead of Yellow at #2-1/4?

Does the application of 18.4 Green vs Blue and 18.4 Green vs Yellow make the applicability of the last sentence of 18.1 clearer?

Bolla, the answer to your question about whether Green has been given mark-room is "no". When she leaves the zone, she is no longer entitled to mark-room under rule 18.2(d), but rule 18 still applies. The last sentence of new rule 18.1 refers to the completion of the process of giving mark-room to a boat that is entitled to it.  If, at some point in that process, she gives up the right to mark-room before she has been given all of it, the last sentence in rule 18.1 does not "shut off" rule 18.   In your scenario, as all other comments say, at positions 3, 4 and 5 Green owes Yellow mark-room and fails to give it at position 5.  

Here is my reading:
When Green enters the zone she is overlapped inside boat and entitled to mark-room under 18.2b.
Green does not sail to the mark but holds her course then bears away and gybes more than 3 boat lengths from the mark.
At 3, Green has left the zone and her entitlement to mark-room under 18.2b ceases   (see rule 18.2d)
However, Rule 18 still applies as all three boats are required to leave the mark on the same side and at least one of them is in the zone.
All 3 boats are now overlapped. Green is on the outside and must give mark-room to Yellow and Blue.
However, when Yellow entered the zone she was overlapped inside Blue, and is entitled to mark-room. Yellow's mark-room included, at that time, room  to comply with her obligation to give Green mark-room (see Defn. Room). As a result, Yellow cannot sail directly to the mark. Blue gives Yellow room to give mark-room to Green
Yellow gives mark-room to Green, which Green does not use. Yellow passes astern of Green and is then free to luff up to round the mark, which she does. Blue gives Yellow room to round the mark and sail the course without touching the mark.
As Yellow reaches a close hauled course, there is contact between her leeward starboard side and the windward port side of Green.

Conclusion:
Yellow, overlapped to windward, did not keep clear of Green and broke rule 11.
Green overlapped on the outside did not give mark-room to Yellowand broke rule 18.2a
Yellow, sailing within the mark-room to which she was entitled  and is exonerated under rule 43.1b.

Davies, maybe in the second line of your conclusion there is an error: Yellow instead of green?

FACTS:

Approaching, at the end of the downwind leg, the left gate mark to be kept at port, GREEN on starboard broad reach entered the zone first. YELLOW, also broad reaching has an outside overlap on green and entered the zone as 2nd boat.

 BLUE broad reaching, on port tack, is  then outside overlapped with yellow and still outside the zone.

GREEN continues her course, passed the mark, sailed just outside the zone, gibed to port tack and sailed in the direction of the mark.

YELLOW, still in the zone, gibed also on that moment and got an inside overlap on green. She sailed in the direction of the mark, but could not sail more to windward, because BLUE sailed between the mark and her. 

While rounding,  the distance from the mark to BLUE was 50cm, BLUE to Yellow 1meter. There was a contact between the starboard aft side of the wing of YELLOW and the forward side of the port wing of GREEN. There was no damage.

 

CONCLUSION:

BLUE is taking room to which she is not entitled under 18.2(b) and infringed so rule 18.2(b)

YELLOW still inside the zone before Green entered the zone again with outside overlap on her, had under 18.2(a) to be given markroom by GREEN. YELLOW could not head up to sail inside this markroom to which she was entitled and broke rule 11,  because BLUE was sailing there. Yellow is exonerated under rule 43.1a

Green did not gave Yellow the markroom to which she was entitled and broke rule 18.2a and 14.

DECISION:         BLUE DSQ  and  GREEN DSQ

Carmelo - thanks for that. I have corrected the text.
Joep - I am not convinced that Blue broke a rule.

At 2 Yellow cannot bear away any earlier because she has to give room to Green. Yellow then manages to pass astern of Green, and begins to gybe, leaving a 1.5 BL gap between her and the mark. Yellow continues her turn luffing to close-hauled, and is still 1.5 BL from the mark when she reaches close-hauled. Blue passes astern of Yellow and sails into the gap that opened up because Yellow was giving Green mark-room, as she was required to do.
There is no indication on the diagram that Yellow was prevented by Blue from luffing faster than she did, nor that there was any reason for her to sail above close-hauled. As I understand it Blue did not prevent Yellow from sailing to the mark. Neither did Blue prevent Yellow from rounding the mark without touching it.
I would argue that space was made available to Blue and she took advantage of the space without breaking a rule. Case 63 is relevant.

Gordon, Thanks for your response.  When I look at the three boats in position 4, then do see that GREEN is pointing higher then YELLOW.  In the drawing it looks to me that YELLOW can not point much higher there, due to the presence of BLUE, who takes that position.  In the drawing it does not look to me that BLUE is taking really only advantage of a free gap as described in case 63. But to be sure we need a hearing. If YELLOW says there is a free gap and could not point higher then I saw the drawing not correct and I have to reopen the case.

My reading of the diagram is that at 4 Yellow is rounding up towards close-hauled. Her trajectory is consistent with the way the other boats are also rounding up. I would need more evidence to conclude that Yellow was prevented by Blue from rounding up quicker.
Green is sailing higher at that precise moment because she started to round up earlier.
But as you say, correctly, we would need a hearing to settle this. However, at least this discussion allowed me to read Case 63 again.

So cool !!!

I have a point !!
At position #4, is Green an OBSTRUCTION for B & Y ?

If YES, does rule 19 applie ?

Cheers !!!

Catalán, refer to Rule 19.1(b). 

In 4, blue compromised by the interior does not have the right to space in the mark with yellow, which is the one who still has it for 18.2 b, yellow also has the right of way with blue for 11, however blue does not violate these rules by "sneaking" through the interior because yellow is sailing outside its space on the mark and even when luffing in 5 being close to a upwind course it is not hampered in its maneuvering by blue.

As for green, he has left the zone, losing his right to space in the mark and upon re-entering he must give space in the mark to both for 18. 2 a, in turn green has the right of way for 11. Green gives the mark space to yellow. Green between four and five has maintained its course without violating 16, so the contact is produced by the change of course from yellow that is not kept separated as it should by 11, also it is not navigating within its space at the mark so he is not exonerated for 21.

Yellow must penalize according to 44.

This is a competitor's point of view.

En 4 azul comprometido por el interior no tiene derecho a espacio en la marca con amarillo que es quien lo tiene aun por 18.2 b, amarillo tiene tambien derecho de paso con azul por 11, sin embargo azul no infringe estas reglas al "colarse" por el interior porque amarillo esta navegando por fuera de su espacio en la marca e inclusive al orzar en 5 estando cercano a un rumbo de ceñida no se ve obstaculizado en su maniobra por el azul.

En cuanto a verde a salido de la zona perdiendo su derecho a espacio en la marca y al volver a ingresar debe dar espacio en la marca a ambos por 18. 2 a, a su vez verde tiene derecho de paso por 11 . Verde da el espacio en la marca a amarillo. Verde entre cuatro y cinco a mantenido su rumbo sin violar 16, por lo que el contacto se produce por el cambio de rumbo de amarillo que no se mantiene separado como debe por 11,  ademas no esta navegando dentro de su espacio en la marca por lo que no es absuelto por 21

Amarillo debe penalizar segun 44.

Es el punto de vista de un competidor.

I think it's pretty clear that Green owes room for Blue and Yellow. I don't think Yellow owes room to Blue between pos. 4 and 5. Blue should get a foul here for forcing Yellow into Green. Yellow is not keeping clear of Green, but is exonerated by new 43.1a

To answer Bolla's question, I think mark-room can only be "given" after the mark has been rounded. In any previous situation, mark-room is still something a boat needs (even if it is not owed) by all parties. Another way to make the case is, you're in first by a several lengths; you need mark-room from the entire fleet. It has not "been given" until you finish rounding the mark, even though all the other boats are able to so without changing their course.

These are my opinions, and I don't have any cases to back them up with.

In the new 2021-2024 rules. A rule is changed concerning: when mark room has been given.  18.2(d)  says now: Rules 18.2(b) and (c) cease to apply if the boat entitled to mark-room passes head to wind or leaves the zone. So it is not anymore when the mark rounding is finished as was in the 2017-2020 rules.

Joep, Yes .. they moved the "when mark room has been given" out of 18.2(d) to a new location in 18.1.  When it was in 18.2(d) it had the side-effect of leaving 18.2(a) still applicable n special instances.

Now that it is moved to 18.1, all of rule 18 ceases to apply once mark-room is given, not just 18.2(b) and 18.2(c).

Angelo,  It tells me that the  text move: "when mark room has been given" to the new location is organising the rule book. But  "When"  is now really described in 18.2(d).  That is very help full.

The last sentence of 18.1 introduces a general condition that applies to the whole rule. Rule 18.2(d) sets out specific conditions for 18.2(b) and (c). It does not switch off the whole of rule 18 so, for instance 18.2(a), 18.3, or 18.4 may still apply. 

Fully agree with Gordon

I agree complete with the first sentence Gordon writes.  But reading his second : "Rule 18.2(d) sets out specific conditions for 18.2(c) and (d)."  I think it should be changed into :"Rule 18.2(d) sets out specific conditions for 18.2(b) and (c)." under the new rules of 2021-2024.

Joep,
I have corrected my error.

Gordon

Hi Giorgio. Long time no see u.
Well, try to cope with the question. 
Back to your first  question about last sentence of 18.1, i would have replied: no, because at pos 3 "mark room" has not been given, see "definition"  of "mark room", point b). Beside any other considerations given, that i red and approve, specially the RRS 15 at pos.5