The UK does not allow reg re-use, ever (unless you rebuild the original plane) but the US does.
For those following this event, there is new information from Croatian air crash investigation agency, the old post about the Pipistrel Virus is gone from their page, and there is now this post:
Regardless of the initial airplane type confusion, it’s a tragic event for the people involved and their families, as well as the GA community and Pula airport. I hope we’ll have the final report soon so that we can learn from this event.
