Real world Vmca varies with CG, but the AFM certification figure is based on worst case which can be presumed to be for max aft CG.
Flap/Vmca and flap/Vmcg relationships will depend on the individual aircraft and, in most cases, the OEM doesn't see a need to investigate whatever variation may exist, certainly not through to defining the data in the AFM.
Stall speed varies with CG and the certification AFM figure generally is based on max forward CG which gives the highest stall value.
Real world Vmcg will depend on nosewheel load, but the certification AFM figure is based on a free nosewheel ie no NWS, although some standards permit actual demonstrations in the wet with NWS.