Oh I have 2 mistakes on 6-5 right now with 4 hexcells away from completing the puzzle. I have no problem going back through that one by cheating/memory because both of those mistakes were stupid oversights, such as rushing and missing a blue hex in counting. those 2 didn't end up revealing anything else to me though. That puzzle is such a ridiculous behemoth that beating it once is good enough for me lol. I have perfected most of the other infinite levels though except for maybe 4 or 5. I'll get back to them.

If you care for the Perfectionist achievement in Hexcells, you can only have one mistake per puzzle. If you finished any puzzles with more the 1 mistake, you have to redo them or the 100% achievement won't unlock.