It's not only true, it just gets worse. It seems that most of the car rental companies use archaic data processing systems that have little flexibility in making changes. Some months ago, I tried to get Enterprise to credit my National account for a rental instead of the Enterprise Plus, and it was so complicated it never happened. A couple of weeks ago, I contacted Hertz mid-rental when I discovered the wrong credit card was used for the reservation -- and there was nothing they could do to switch the card unless it was at the conclusion of the rental. And the list just goes on and on and on.

I'm not sure if the rental companies use outdated systems to their advantage, or if these are actually newer data processing systems programmed to behave like ancient mainframes. In any event, the issue you've raised is quite true and is pretty much across-the-board in the car rental industry.