Thanks for the tips everyone. Unfortunately I was definitely talking about a 2 mm difference. This all happened rather suddenly it seems, but I definitely have yanked and pushed on the extruder a few times to free or feed filament, so I suppose I could have bent something. One possible corresponding thing I forgot to mention was that I recently changed out all the bed leveling nuts with wingnuts. I checked, they haven't fallen off or anything, but I wonder if it's possible they're not holding as tight as the originals?