Graynomad:
If address pins are missing you will have holes in the space that would cause duplications on top of other data.So for example if A4 was missing you could write 16 contiguous bytes ok, but the 17th byte will go into location 0, thus overwriting the first byte. This could be manageable but a right PITA.
Likewise with data, the top bits may not matter if you stick to values below the first missing bit, but if you are missing any low-order bits you will be in trouble. This is almost not possible to use unless you "adjust" every variable you save and "unadjust" every variable you retrieve.
Rob
I don't think missing address pins cause other problems than a smaller device. For instance a 65000 byte device with 16 address bits. If leave one address pin/bit out, you'll have a device with 32000 usable bytes. If it is a some kind of rom and you connect it to a processor with all address pins, then you'll get gaps (or a great mess, if don't take care). I am not going to draw any truth tables so I leave this here.