Hi Jason,
Firstly, a big thanks for all your real efforts in helping collectors everywhere with your detective work and on moving this forward.
However, a few observations from my part.
Firstly, I don't think you can assume just because a genuine used/torn cardback displays the 'twin stem' non sealed areas on the card that it had a twin stem bubble. This genuine sealed Hoth Han 65 back D Palitoy that I have from childhood shows that it has been factory sealed in the machine/die which was obviously set up to
hold and seal both double stem AND single stem bubble stock - note the double stem 'gaps' in the seal. If this were torn from the card by my eager hands in the 80s, it too would display twin stem non sealed gaps and let us believe it would have had a twin stem bubble.
Also, do you have a measurement for the 'super wide' toni bubbles? My Obi Wan also bought in the 80s has the squareish corners, and is very clear, just like my hoth Han, but is a wider version...
My Han Hoth is: 96mm high by 35mm wide approx., slightly wider where it meets the card.
My Obi Wan: 98mm high by 42mm wide approx, slightly wider where it meets the card.
Another real sign of a genuine seal for me is the slight inside edge card 'pullback' from the sealing process - evident in both the above genuine figures. Note also I've highlighted this on used cardbacks (excuse my dodgy shaky Paint hand drawing!) that displays the same trait. It's hard to sow in photos, but look at the right had edge here -
Shown here also:
Hope this helps.