Glad it helped a bit Oli.
You needn't worry too much on Meccano/PBP bubbles appearing on Pal ROTJ cards because it won't happen.
If you were talking Trilogos on the other hand then it would be a different story..get ready
A good (and confusing) example of what I mean is this:
Three different Trilogo variations but all three seemingly have (although I can't confirm all three are an
exact match..only measured two!) the same bubble.
One is considered German (or Parker produced), one is Palitoy and the other is 100% Meccano origin
Back to Palitoy ROTJ cards...the "Kenner-esque" Madine bubble is just a term that I made up as it looks like a bog standard US Kenner bubble, it yellows, it fits and does the job has the waffle pattern yada yada.
Overall, there are plenty of bubble variations on Palitoy ROTJ figures and all have their pros and cons. If I were putting together a set I wouldn't worry too much on what I had (because I am fine with Trilogo bubbles even though being so big they can allow the figure to get damaged and be dented themselves) but I would try my best to stay away from double stems. They look **** hot but they can break/split/lift on you and that hurts!