ssj- That's what I was going to try, so it's good news that it's a tried-and-true method! I think I'll try to modify the case a bit so I don't have to scan through the plastic window; the ones I have are pretty scratched up.

ICEknight- I thought maybe it came from the patent wrapper. I'll have to look up some other Canadian patents and see if they have more info than the US ones.
The backgrounds in the games I have weren't cut very accurately- some of them aren't even cut straight. So it's very likely the backgrounds can wiggle around a bit.