Hello gentleman,
I believe the min ACC ALT of 400 ft is just a regulatory requirement.
The "global set of points" probably is opposed to "single point calculation". The latter term is being frequently used in PPM for PEP/LPC calculation, meaning the values and their extremes / limits are valid for one initial input data [as in one box from an RTOW chart].
The V speeds limiting values as well as the ACC ALT values shown on the bottom of the chart need to be valid for any possible entry and all results from the table above, so naturally they are the most conservative ones. I think Thierry is trying to say that the dislayed limits are valid for the full table in general - "wide range of possible calculations"
That's the best I can make of it. Sorry for the broken English on my side.