You’re right that the airline can’t make their own rules, but all it takes is one or two uninformed airline employees to mess up your trip. I stick to the six month rule for our passports just to avoid a situation like that. Now if I were I in OPs position I would take your advise and bring a print out of the rules. A bunch of people are going to reply saying it’s never been a problem, but better safe than sorry.

(Flashback to summer 2021 and me arguing with a AA agent about the acceptability of our COVID tests, even though SXM has already approved them. Fortunately I had two different tests and she was happier with the second set.)