Thanks all for the useful replies. I was not trying to game the system, I only updated from c11 pro to c14pro because of the usb elicenser support coming to an end(?) and wanting to stay on the upgrade path. I had no real intention of updating otherwise.
I just thought by chance I would have had c15 pro in my list as “I thought” I hadn’t used the DAC…however…
….apologies to all, I did enter the DAC 
but totally forgot about it, and I even screenshotted it! 
But I think I entered it in a bit of panic at the time. I would have happily not have entered if it meant I would have held on to the grace period.
Oh well mystery solved. Again thanks for the useful advice and please forgive me for wasting your time. 
I feel I may still have related questions however…