FF:
The Flight Manual phrase is "Max Demonstrated" and I have always read and been taught that it meant what it said on the tin - the max that was demonstrated during certification testing. There must obviously be a structural limit (that varies with mass) but this is not directly related to max demo'd xwind.
BTW, I believe that FAA certification before the 60s/70's didn't require xwind capability to be demo'd but that there was a requirement that handling was "safe" down to 20% of Vs.
HFD