I’ve been lucky with buying secondhand copies of Trainz. All the ones I have have never been registered or if it is even possible the previous owner got them “de-registered” before trading them in. I’d suggest if the seller is an individual like on Ebay, etc then try asking them if they ever registered it. If they can confirm it has been unregistered then you’re in luck. I asked somebody who sold me my copy of TRS2006 and they said they had absolutely no clue what I was talking about.