So, a long metal tire lever got it off in the end.
Yay! Good on you; it surely took the effort!
Some tire and rim/tape combos just fit extra-tight...an aggregation of tolerances, methinks.
I usually have good luck by pushing the bead into the rim well, but when the last bead is stuck fast, well, that's a tough one 'cos it is so hard to get a tire lever beneath it and you're effectively working from the "wrong" side. I've had remarkable luck with mounting and removing difficult tires using my ancient VAR tire lever/tire jack combo. It is a wide, cream-colored nylon affair. I got it back in the day to help mount the newly introduced narrow, high-pressure Michelin Elan clincher tires (for which it was partly developed -- "Rides like a tubular" was the advertising tagline. May have ridden sorta like a heavy sewup, but boy, did it de/mount differently). Man! Those things clung like grim death and put up a battle going on and coming off. The VAR did the trick each way, though. Why it never folded or snapped is beyond me. Good nylon, I guess. If you can still find one, a real aid for those who use skinny tires.
Glad the long metal lever worked for you. Might be worth tucking it in the underseat tool bag?
Best,
Dan.