Can you elaborate more on the "one euro size = one us size" not being the case with Vass, if you happen to know? Would a whole size up in Vass translate to less or more than 1 full US size differential? And would that be true across the entire size spectrum, as in going from 40 to 41 and from 45 to 46 be the same difference in US sizing?
I think, if you ignore the inconsistency between different pairs on the same last for a second (if it can be ignored), this may be the answer but in trying to keep things simple, they don't tell us what we really need to know that would help us tremendously in picking sizes. Also I remember in the past when I asked for sizing by email, the answer was different from the charts they have on their website. I find that their charts are wrong, if you go by the charts you will end up getting a shoe that is too small. That might also depend on the last, which of course their charts does not consider. For example, is there really anyone here who wears a John Lobb 10UK say 7000 last who can fit in a 44 Vass U last?