My replacement screen came with a blue plastic on the back, which I removed. However, there was also a black sticker underneath that, which really wanted to come off with the blue piece. I couldn’t tell if the black film/sticker should stay on or if it should be removed. The original didn’t seem to have that, but there were other non-insignificant differences between the two which made me not really trust that comparison as an indication of what I should do.
I left it on in the end, but the screen doesn’t really want to sit down flush. I’m wondering if this thin film is part of the problem since every tenth of a millimeter matters with these things.