Maybe Gendan the UK approved re-seller should say on their website that registration cannot be transferred to a new owner, and it's a pity that they do not offer the upgrade option that you do.
Have you asked them directly? Alternatively, have you asked Ross-Tech in the US if they'll process your trade-in if it was bought from a reseller? Respectfully, the way you have phrased certain things has the air of complaining rather than seeking solutions. Feel free to correct me if I'm wrong.
All the other auto diagnostics vendors charge for annual updates and support. Ross-Tech offers free updates always, lifetime support to the original owner, and lifetime support to a second-hand owner for a one-time fee. And if you want to trade-in your used MicroCAN interface for a HEX-USB+CAN, they're only asking for the NEW price difference plus $60 USD. How the heck is that a bad deal?
Yes, I do drink the Kool- here, but it's tasty and refreshing. Try it!
Jason