Direct entry Airman Aircrew (me) in the late 70s entered on an eight year* gratuity-attracting, non-pension engagement. All as per the contract. In my 50s I was told on at least 3 occasions that I WAS entitled, received forecasts etc, only to be told , "Oops, we made a mistake..." I was a bit cheesed, but I didn't lose anything I was entitled to, so like the Murphy's, I'm not bitter!
CG
* I believe 9 years was the minimum, so anyone signing on moved over to '75 after a year. I don't know of anyone other than me who walked at 8 years...