I agree with your analysis of what rules apply.

Starboard is sailing his proper course which is up and down based on the wind. For most of the time period in question he can do what he wants. (he can't be accused of hunting a port tack boat) Port simply has to adjust as best he can.

IMO... S's obligation to give room to keep clear comes in the last few seconds... when in this case he dramatically altered course to avoid a collision. What could port EVER SAY in this circumstance.... IMO, His only argument would be... I was clear... the change in course was unnecessary. He would need more evidence to support the claim he was clear and S's change was unnecessary.

What am I missing?