The mk1 could be taken to 16MB (4 chips on the underside of the board) but mk2/2a don't have such facilities; the factory complained that they got solder bridges on the unused pads when flow soldering the through-hole stuff.

Very brave/stupid people could do things like stack ram chips on a mk2a, but you're really have to want 32MB *A LOT* to risk it!

Hugo