After going through all your replies, I can see what I have is an 80 percent scanning problem and a 20 percent organizing problem. It used to be easy for me to remember where everything was or at least have good guesses. But I can't remember anymore because there are too many items from too many series from too far back. I end up going to through most of my stuff each time I need to find just one item.
As far as my "stacks" go: I don't stack my things too high because the weight would squash them more together. I don't put similar series cels/sketches together because I would have to remove the packaging that keeps them out of the light. I'd hate to leave them out in more indirect light than I have to since I've even seen my NON-production artwork papers fade in indirect light after some years have passed (the part that was sticking out in the light I mean).
I did go and label my ITOYA folders spines with the names of the series in the folder. That'll help me if I'm looking for something in those. It used to be easy to find a sketch, but I have too many sketch sets from several times more series than I did eighteen months ago so "memory" is no longer an option for me.

Say Krafty, how does that file cabinet you put your sketches in look like?
Sketch sets are definitely harder to keep organized than cels. I should find some way to display my favorite sketches in folders while keeping the sketches I don't like as much somewhere else (without throwing them away). Then I'll need some way to remember which separately displayed sketches go with what extras/repeats sketch bag they came from originally.
