Must use the correct CPS.
My previous employer is going through this right now. I helped them migrate to MotoTrbo XPR4550 and XPR 6550 radios. Company policy was to load all of the radios (about 1400 of them) with the new CPS anytime Motorola came out with a new release.
With releases becoming more common, this took a lot of work. Then anytime a radio was repaired, Motorola put the latest software in them. This forces you to get a current CPS version. It is a marketing and license strategy to keep people honest.
So you must use the correct version of CPS or newer on a radio. And like a previous poster said, there is no official way to go backwards.
This previous employer of mine was also warned about XP computers coming to the end of their service life and how Motorola was going to stop supporting XP when Microsoft ended support. I bought two Windows 7 computers, and then got chastised for that. Now a year later, they find themselves having to buy Windows 8.1 computers that are actually a little finicky with Motorola software, as well as the Telex dispatch software they also run.
As a radio shop owner told me once, you end up looking like a computer factory if you support several series of radios.
