I mean that, if you were to try to trace a straight line through the hinge slots, the "slanted" one would not be parallel along that traced line (it would instead intersect it at an angle). That's on the wing... on the aileron the slots are all straight. In other words, if I were to force the aileron installation without fixing the slot, on one of the CA hinges, there would be a significant twist causing the aileron as a whole to not move very freely at all. The servo will have to struggle with it much more.

edit: I just remembered that Great Planes brand CA hinges are a lot thicker than Hangar 9 hinges. I think I might have some GP brand hinges around here somewhere. So if I end up loosening the slot in fixing it, maybe the GP brand hinge will still fit tightly. Anyway, if you know how the related wing structure on the mini showtime is (descibed in 1st post), you'll see why you can't just cut a new adjacent slot.