> I couldn't find any legit reasons for keeping the "six-month rule" around but it seems like it's still occasionally checked, sometimes even during boarding.

Airlines sometimes check for things during boarding. Those things are never rules outside the context of the airline.

I had an airline require once that I complete a form before boarding that, by the terms printed on the form, expired before the plane landed. That didn't matter to them.

Airlines are clueless. I don't know why they do their imaginary checks.

> Airlines sometimes check for things during boarding. Those things are never rules outside the context of the airline.

Nope. Plenty of countries still require 6 months' passport validity to enter.

> I had an airline require once that I complete a form before boarding that, by the terms printed on the form, expired before the plane landed. That didn't matter to them.

> Airlines are clueless. I don't know why they do their imaginary checks.

The airline doesn't give a shit about whether you can legally or practically enter the country they're flying you to. They care about whether they're going to be held liable to repatriate you at their own expense, and their processes are set up to ensure they avoid that. If the requirement on them is that they check your document before you board, they'll check your document before you board.