I have been in the same situation. The answer is B did not have inside rights, but A needed to close the door and not allow B inside. A did not have the right to tack on B, even though B should not have been there. A should have protested B. 

For Scenarios #2 and #3 ... food for thought ... 

As the boats tacked 18 would be off and if neirher down to clossehaulled the they are tacking at the same time so the boat on the right is in the right. 

Here's what I'm getting at .. in any of the 3 scenarios, is the inside boat entited to MR after they both are past HTW?

If so or not, why or why not?

In Diag A, boat A with mark room has not yet passed the mark nor left is astern, so 18.2 still applies and A has mark room. The diagram does not go far enough to see what happens next so it is not shown to determine if B breaks R 18.2.

In Diag B, boat A luffed up as she is entitled to do with ROW R 11 and mark room, and Boat B also began to stay clear by luffing - then Boat A passed HTW, turning off 18.2. . After A passes HTW, B also passes HTW in an attempt to stay clear.  A breaks R 13. B breaks second part of R 13 but is exonerated under R 43 as she was not given room to stay clear.

As the boats were rounding a leeward mark R 18.3 does not apply, They were starting the next leg which is a beat to the next mark which is to windward.

John

My reasoning is based on the comments in Scenario 3 of the Appeal 130, and in Case 118.

There is also a case where a boat on stbd is reaching into the windward mark, and the comment says that it is still a beat, and the boat has overstood the mark. I see your example in diag 5 as just the reverse and apply that same logic. Boat A is rounding a leeward mark but has sailed deep.

John