But these pricing models are dumb because they create the incentive to invalidate the pass. And that was inevitable.
The problem here is that the airline invalidated the passes for behavior they enabled such as making multiple bookings at the same time (ie booking agents would tell them to do this and make the bookings for them).
Also I know selling your commission seat or transferring the pass was against TOS but one example quoted here of approaching people at the gate to use the companion fare wasn’t against TOS AFAIK as long as no money changed hands.
Also it’s worth pointing out that these passes cost serious coin back in the day.