Vmcg is discussed in the FAA AC 25-7A
http://www.airweb.faa.gov/Regulatory...A?OpenDocument
One observation about laptop performance systems is that they sometimes utilize "look-up" tables vice the perfromance graphs found in AFMs. Not sure that is the case here. Also, the rationale for the performance numbers is sometimes based on additional considerations beside the actual test data. For instance, a control system limitation, hydraulics, etc.
The other factor for consideration is performance requirement in place at the time of certification. This information can be determined from the Certification Basis in place at the time of certification. AC 25-7A is current information. The Type Certificate Data Sheet will document the certification basis for any aircraft.
http://rgl.faa.gov/Regulatory_and_Gu...e?OpenFrameSet
I agree about seeking help from Airbus. And, simulators do not necessarily model runway dynamics as well as one might like. If you review the FAR Part 60, you will see that the simulators are centered on training (procedural) vice an engineering simulator at the manufacturer.
Hope this helps.