Airlines use the IATA Portal to check these matters when you check in.
Here is an example, for my late trip to Thailand . I present my Passport to the Check in Person. They put in my details and they know what flight I am goin out on and the one coming back. This shows them that in my case it was 29 days in the Kingdom.So that meant I was with the rules of "POOT" At the same time it tells them I do not need Visa . It also tells them that my passport is good for travel.
Some years ago a person from Australia was in real Panic on Saturday, was flying next day and had less than 6 months. I did a double check even though I knew the answer . Just went in the IATA Portal put in deatails , it popped up clear to travel.