Depends on how the developer manage the demo licensing, like URS, they'll provide the demo for you over and over again to the same ilok account. Whereas company like Waves and McDSP only provide once to the same account.
But I don't think that's what peeder was asking, I think he mean if buying a 2nd hand ilok with say 40 expired demos on it I don't think they can be wiped off, they can only moved to another ilok to free up spaces. lol guess I better order a brand new one or else if I receive one with 80 license on it I'm gonna be

like hell...