From the FAQs on Revo's website:

Is there a way to undo an uninstallation of a program?

Reinstalling the program is the first and easiest solution. Because Revo Uninstaller Pro automatically creates a System Restore Point before uninstalling a program, you can use the System Restore feature to restore your system to a previous state. You can access System Restore in Revo Uninstaller Pro: click Tools -> Windows Tools -> Windows System Restore. By default, Revo Uninstaller Pro moves all leftover files to the Recycle Bin when you delete them, so check there for accidentally deleted files. Also by default, Revo Uninstaller Pro backs up every deleted leftover Registry item, so check the Backup Manager for any backups of deleted Registry entries you want to restore.

Therefore EricNZ's suggestion seems to be an achievable option.

I don't have a restore point, but a system image from June. It will be a bit of a hassle as I have to reinstall another NLE I have and hardly use. I'll dig in the registry first.

** I found an error, C:\Users\___\AppData\Roaming\VEGAS folder is missing

Before restoring I'll get it from my W7 disk and see.

** I found an error, C:\Users\___\AppData\Roaming\VEGAS folder is missing

Possibly Revo is too aggressive in its cleansing. Maybe just use Windows Apps and Features uninstall as a first approach.

Well, it's too late for me Dexon. Re-copy the missing folder didn't help.

I'll re-image tomorrow morning when it will be just a bit less hot and humid...

Thanks guys, Let it just be a warning for others

@FayFen I had the same trouble using IObit Uninstaller. Uninstalling one version with it messed up my other versions. These deep cleaning uninstallers are far too aggressive. I restored my other versions by re-installing them and doing a reset and clearing of the cache. As @Dexcon pointed out, use Windows Apps and Features to uninstall.

I've been aware for a while that different VMS versions share Render Templates. But looking at my User\AppData\Roaming\Vegas I see there's more. The 'Movie Studio Platinum' folder for example doesn't distinguish between versions. But it only contains Favorite Plugins.

Revo works just fine for this, except I don't recommend using Advanced mode.

Really, there is no need to remove 16 right away, I would eave it there for reference, if nothing else.

Fayfen said he removed 17 trial.

Oh, thanks. Same thought though.