i feel like groups only get multiple versions and more than 1 c/w in a single if they manage to sell a good amount of copies the previous single.
its like an award for selling well.
proof of this is Berryz and S/mileage.
Berryz has 3 or 4 version of a single and only 1 c/w every since these 2+ c/w have started in H!P.
and S/mileage lost the extra c/w they used to get after they started selling a lil bit less xD
MM and C-ute who have had pretty awesome sells get 6 or more version of a single and multiple songs.
they need to give the other groups the same amount of treatment so they sell good too