Try a search as this gets reviewed regularly.
(a) old UK BCARs had a 7kt Vmcg
(b) otherwise generally nil wind
(c) the certification number is a line in the sand for AFM purposes.
(d) real world Vmcg will increase for adverse crosswind (UPWIND engine failure is the problem .. think about it .. gives an into wind yawing moment due to the thrust asymmetry and also due to the weathercocking)
(e) increase varies with Type but typically 0.5 to something in excess of 1.0 kt/kt.
This increase doesn't invalidate the AFM data .. but it sure does need to be considered by crews if you are very light and have an aft CG .. ie short range ferry operation. It is quite easy, under such circumstances, to find yourself in a Vmcg departure situation with a failure near V1.
One of the other considerations is training .. I did some work for one operator which routinely used quite high V2 overspeed schedules but also had a short ferry operation which they could do at min speed. A few sim exercises opened more than a few eyes to the problems.
Unless there is a dollar in it for the OEM, I wouldn't necessarily take the view that the OEM will put non-required fat into the aircraft design ...