Hi Gav, fortunately, I've got all the licenses for all my Lightroom upgrades going back to version one. The main issue yesterday was Adobe decided to turn my "owned" version of 6 into a trial and put into a restricted version (ie: no develop module) and the program was stuck at Lightroom CC 2015. The crux of the matter is one still has to have an Adobe account whether you want one or not. I signed out and back in again, then went through the rigmarole of entering serial numbers for my paid for upgrades, at which point the program hung on the authenticating screen, so I shut it down and reopened it, and voila, Lightroom 6 is now in the top left of the screen.
Every photo that has been edited is still there but the history has gone completely. It's literally like starting from scratch again, as Lightroom has to build a new catalog. For some unfathomable reason, my backup catalog kept shutting Lightroom down with the error message "Lightroom has encountered a problem and needs to close."
Adobes answer to my furious enquires? Their response was, we'll give you Adobe CC free for 3 months if you stay with us. Ehh, no thanks! So they took £68 out of my bank account to close my contract!