Yes, it is proof for that drive. And for a good many others. They were designed, manufactured, and put into operation. Individual drives with specific requirements. A particular application was in the water industry which required no negative efficiency tolerance. It's a bit of a challenge.I haven't looked at the numbers, but it may be proof for that one drive. That doesn't mean it works for all drives. Proving that would require a general argument along the lines of what Carultch or I gave.
Anyway, that's what what I did for a living.