All the airlines have numerous unofficial policies like this, and typically, the people at the airport have a great deal more discretion and flexibility than do telephone reservations agents. It is often to a pax disadvantage to call phone res because res sometimes annotates a pax PNR (reservations record) that the pax was told whatever the official rule is.
The "flat tire rule," generally allows for a pax to be accommodated if arriving with in 2 hours of scheduled departure. Most all airlines have a flat tire rule, but I'm not sure if its really written anywhere or if it too is an unofficial airport procedure.
And ot from this thread here is an NY Times article about
Double Double Secret Unofficial Airline Elite Levels. In my travels, I have come across the secret lounges discussed in the article.