1. - U = shortened, N = scope plate, S = folding stock, M = modernized.
2. Almost everything is in one way or another different on the AK-47 and AK-74. The AK-105 is basically a 74 with a full folding polymer stock and foregrips, shortened front end (unified front sight and gas block) scope plate, and smooth, flared over safety, top cover. Other small differences exist.
3. There are no Soviet underfolding AK-74 variants, except one of the very first prototypes.