the VST system maintains internal names for the plug-ins,  this is a developer design decision, whether to keep them separate and to what level).

The DAW is actually responsible for removing duplicate versions of "found" VSTs and better DAWs offer choices.

Did you do a VST rescan after update? Some DAWs have full rescan and "fast" rescan (differential).

And no need to rename .dlls, because again, VSTs have internal IDs (names) that have priority over file names.

This may have been brought up in the past, but it is an issue that is an endless pain. I've had Pianoteq since version 1 or 2 and have used it in endless DAW projects (it is in my templates, so literally EVERY project has Pianoteq in it).

The issue arises from the endless string of versions makes the prior version no longer work in these projects, as they are unique DLL's. I used to do a very clunky work around this by keeping all the old versions installed simultaneously and adding renaming the current one withsimply "Pianoteq.dll.

It seems insane to me that the new version doesn't simply replace the old one and maintain some sort of backward capability.

I've got a new DAW PC and I don't have any of the old versions installed. To even open any project from 1,2, 5, 10 years ago that contains Pianoteq, I literally have to first manually replace the VST synth with the currently installed version, but then I wipe out any reference to which piano was used, settings, etc. It is such a workflow drag and mood killer to have to do this each and every time. Am I alone in this issue?

You are not alone, I can certainly sympathise.  I wish it worked that way but I imagine that's problematic.
The system isn't perfect. I would rather be sure I was getting the latest, or the old sound though. I only came in with version 5 to be fair. You'll have a few more versions.

I make templates with external plugin FX (ITB plugins - just not inside Pianoteq) then occasionally I update those old templates. That does get a little tedious but it's not the end of the world.

Another option is to freeze tracks more often rather than relying on MIDI files, but turning tracks into audio from midi will inevitably use more drive space.

The issue arises from the endless string of versions makes the prior version no longer work in these projects, as they are unique DLL's. I used to do a very clunky work around this by keeping all the old versions installed simultaneously and adding renaming the current one withsimply "Pianoteq.dll.

It seems insane to me that the new version doesn't simply replace the old one and maintain some sort of backward capability.

I've got a new DAW PC and I don't have any of the old versions installed. To even open any project from 1,2, 5, 10 years ago that contains Pianoteq, I literally have to first manually replace the VST synth with the currently installed version, but then I wipe out any reference to which piano was used, settings, etc. It is such a workflow drag and mood killer to have to do this each and every time. Am I alone in this issue?