HCA: Hermit Crab Association

I have 6 crabs in a 55 gallon tank -- I have 3 out and active most nights, but the other 3 haven't been seen in a long time -- as in, I can't remember seeing them this year! There is no "dead fish" smell, or anything else I've noticed, it still smells fresh, heat and humidity are good, fresh food and water, moss pit, good substrate (although hasn't been changed in a year since they moved in there), tons of shells - as far as I can tell, really good conditions.

At what point (if any) do I go digging? All missing crabs are PPs, each has had at least one successful molt with me.

Are you sure they aren't coming up in the middle of the night? Is it possible they've changed into shells similar to the out-and-about crabs and are being mistaken for them? What size are the missing crabs? As you know, large crabs can take forever and a day to molt and small crabs often pull back to back molts.

One of my medium PPs, King Felix the Pale, has been MIA since March but there's been no "wrong" smell in the tank so I'm hoping he's just doing a mighty molt deep down in the back of the tank. If I were you, I'd wait another month and then, if you've ruled out sneaky 2:00 am raids and switched shells, then go look for them.