why do u need covers for some of the MCN's? or are they just for flats???
Fitted MCNs generally have no waterproof layer and require a cover.
Night nappies also, you tens not to want to use PUL over night so most are fitteds, and wool covers work best for night time

AIO - All in One these dont need covers
AI2 - All in Two, this is a cover and a snap in insert. Sometimes the snap in is included in the price others you need to purchase seperately

Pockets - I dont think these need covers, none of mine do anyway.