The Mick Rock photos are some of the best references next to the film. You get a really good look at Frank's left arm in the film, but only a couple glimpses of his right arm. Not sure how the patches were attached to his jacket - but you can tell in some of the Mick Rock photos they are barely hanging on. If the patches had an iron-on or adhesive backing they may not have sufficiently adhered to the leather.
That 'mystery' patch on the back? I'm still leaning towards an adhesive residue or damage from a patch peeling off. You can see plenty of details in the rest of the patches while that one is just devoid - you can even see the white dot in the middle of the "Club Rock-n-Roll" patch, so if there were letters or graphic details on the 'mystery' patch they would be visible in 4k resolution by now.
There are some great adhesives these days, but the best way of attaching patches is to stitch them down - and you'll probably need to take it to a shoe doctor who can do it with a post machine - it's a machine designed specifically to reach tight places and can sew through leather with no problems.