1. Yes, rule 18 grants the right for WI to luff as needed to finish, since this is part of her right to mark-room at the zone, which entitled her to sail her proper course to finish as soon as possible. Her luff at 1 boat length from the mark (position 3) is permitted under rule 18 but is limited by rule 16.1 (changing course). Since the sudden luff by WI did not give LO room to keep clear, she violated rule 16.1 (but LO did not protest and there was no injury or damage). Moreover, the contact did not occur while WI was still racing. She had already crossed the finish line and rule 18 no longer applied since, by definition, she had “finished.” The protest by WI of LO is not upheld.

1. The diagram shows that LO gave mark-room to WI. At only 1 boat length remaining (position 3) LO need not anticipate a sudden luff by WI and was not obligated to fall off to keep clear of WI, as she was also sailing her proper course. At position 4 when contact occurred, LO has also just finished and is no longer racing.

1. No. By mark room definition LO only owes WI "room for [her] to leave a mark on the required side." If WI continued sailing her course from position 3 onward, she would have left the mark on the required side. WI's proper course is not relevant here.
2. Yes.

Part A of the definition of Mark Room includes: "Room to sail to the mark when her proper course is to sail close to the mark" therefor if she is sailing her PC and her PC is to sail close to the mark then should be give such room to sail close to the mark

1. Blue has the right to head-up to the mark just prior to the moment she crosses .. that's part of the 'mark-room' she is entitled (assuming my caveats above).
2. Once she hears her crossing signal, Blue needed to stop changing course if it would have caused contact as she is no longer sailing toward the mark .. at that point her only need is to clear the finish-line while keeping clear of Yellow. If the contact happened after Blue's crossing-signal due to Blue's continued course change, then I don't think Blue can be exonerated.
3. If Blue headed straight to the mark once crossing the zone, luffed at the finish and transoms touched, Blue is exonerated and Yellow did not provide adequate mark-room.

The mark-room that P was required to give S was the space S needed in the existing conditions to sail promptly to the mark in a seamanlike way.

That space was a direct corridor from S1 to a position close to and alongside the mark on the required side. P gave S that room. However, because S had right of way she was not required to remain within that corridor; she was permitted to sail any course provided that she complied with rules 16.1 and 18.4.

Can we agree that at position 2, Blue is not sailing within the mark room she is entitled?

1. that Yellow may or may not have provided enough room, but it's hard to tell as Blue blows his advantage in the argument by sailing away from the mark and so close to Yellow that neither has room to maneuver.
2. If Blue sailed directly to the mark, rounded up and hit sterns before her whistle, then Blue has a strong case that Yellow didn't provide enough room.