I have been testing a system with PDMLink 11.0 M010, and I applied CPS4 awhile ago because I had read the FAQ about CPS which states "Customers are strongly encouraged to schedule regular CPS updates...". Applying CPS4 has left me unable to update to 11.0 M020.
While attempting to update to M020, I finally found the installer log file in the system %TEMP% folder, and the installer log notes that only M010 installations up to CPS3 are compatible for update to M020. Surely, this must be a mistake, I thought. Oh, no, it's not.
I went and downloaded the latest Supported Upgrade Paths document from 11/29/2016, and sure enough, M010 CPS4 and CPS5 are not supported for update to M020. Furthermore, I see that there are A LOT of dead ends in the supported upgrade paths. If you've been patching a 10.2 M030 system with the latest CPS, you're probably in trouble without an old backup to which you can revert.
The Release Notes for the CPS and the Update Existing Installation Guide make no mention of this dead end potential. Only the Supported Upgrade Path document gives any indication as far as I can tell.
How can PTC strongly encourage customers to apply CPS regularly and not immediately follow that up with a strong encouragement to take and indefinitely preserve a backup of the system to guard against potential update/upgrade dead ends?