Yes, under proper circumstances with cards registered at that time, that is correct. What I'm saying is that if those plugins were purchased later on, with later versions of the software, the authorizations will not show up in OS9. I have every UAD plugin that will run in OS9. I can take that UAD-1 card I have and put it into an OSX machine, or a PC, and it will see all my plugin authorizations and I can use every single one. But under OS9, only some of them see authorizations, and that's because it was a used card that I bought off ebay that was an original mackie version with some extra plugins, and at the time I bought it, I did not own all the plugins that would work on OS9... I bought them later and that was already at like version 5. The authorization mechanism changed at some later point, and the new authorization files will not load in the OS9 software, and you cannot get an OS9-compatible authorization file from UA anymore.
if i put either of the two other cards I have (which were bought new), they wont see any authorizations at all, even the mackie-included plugins stop working.
Unless the guy you're buying from can tell you he bought them "way back in the day", its a gamble to say if they will work.