Effectively: Software mechanisms are not the litmus of legality, as if you buy a working key, it may not be legal to use since there are country restrictions.
So I would surmise the opposite stance: if you have a license sitting on a shelf and you "assign" it to a system; using a keygen at that point is fine, since you do own a license and you are not oversubscribing it.
IANAL, but one or the other must be true.