Wrong, at least partially.
From my experience, I never had to uninstall any TINCS to have multiple versions (including going from 3.9 to 3.6).
Basically I just moved the folder somewhere, renamed it to add the version at the end of the name (or whatever you want, but the version makes the most sense), install the other version, rename it to, and then move back the other folder.
If the installer still complains, zip the version you want to keep to make a backup, uninstall it, install the other, then unzip the older.
For some time now I've had 3.2, 3.6 and 3.9 simultaneously without any issues.
But if you have any issues related to licenses themselves, then yeah, just ask TI-Cares, they take care of that well.
