Having seen Vass at Sky Valet, I would think a retailer would be advised to pick 2 of the lasts and stick with those, say the U-last and the Peter or P2 last. Much beyond that and it gets confusing to the consumer (and perhaps to the salesstaff too).
I understand what you're saying, but I don't entirely agree. Yes, it's probably too much to ask that a salesman be familiar with every single Vass last, in addition to all of the lasts used by the other manufacturers that a shoe store carries. However, two lasts, especially given how much the various Vass lasts differ from one another, is really too restrictive. At the very least, I'd carry Budapest, P2, and U.
Perhaps they should follow the Berluti route and only recommend people with certain width feet to certain lasts. For example, I would think that the U-last is best fit on those feet narrower than E-width.
They have to do this of necessity. Like Berluti, Vass doesn't do widths in their different lasts, which means that if one last isn't the proper last, they have to switch to another one.