Hi Ryan -
That is true, yes. And you don’t have to deactivate anything - you are allowed to run Rhino 1 and Rhino 8 on the same machine at the same time.
A legacy Rhino 5 key can be obtained if a user has a new (i.e. not an upgrade) Rhino 6 or 7 Commercial or Educational single-user license - Rhino - Downloads
It didn’t sound like that was the case here though…
-wim