It very certainly wasn't standard procedure. I worked with one man who was born in an airplane-a commercial airliner while his mother was a revenue passenger-and know a woman who was born on a contract charter flight. The man who was born on a Constellation got a certificate signed by Kelly Johnson and the airline CEO, the woman got nada. I suspect that the airlines did not want to encourage pregnant women to get on board hoping the pressure drop would induce labor (which it does very well if she's ready.)

There were quite a lot of those back in the recip era because the pressure differential wasn't very high, the flights were long and the vibration may have had an effect too. Stews got a fair bit of training on procedures when it happened.

The closest thing to a golden pass in airline industry is the retiree Space A privilege, which is as it states, space available. That was once a plum and today it's usually a pain in the rear end as you have no idea when you will get back. Active flight crews have dead head privileges but they are well policed-it's for domicile to duty or other authorized use only. ((Space A on military aircraft is a lot better deal today, I think.))

Certain FAA people have jump seat privileges which on some equipment are good because there is always a seat and it's not a rear end killer. On most it is.

Some executive retireees had a benefit that was simply a credit card (it billed as a Visa or Diners or whatever) that gave them a certain number of flights or dollars per year for air travel, but the company was billed for and paid it so it really was not non-revenue.