... Compare it with the first spot again. (Ctrl-Z, Ctrl-Y x10). Rinse and repeat, for many, many pixels,
How about cloning the part of your piece you're working on let's say 4 times, and do edits on each clone, forbidding yourself to use CTRL+Z at all ? At the end, you've got a sufficiently small number of variants to choose among (maybe some cut-n-paste needed to merge head of clone #2 with legs of clone #4, etc.)
