In the vast gray area of who built what and for whom...there is one guiding light. LOOK at the bike in question.
It might not be the answer to make you all warm and cuddly about the myths or history... but it gets back to what some of the early members of this list have always said...check the work. I'm sure everyone has good days and bad days, and all that, but in the end, if Ugo De Rosa built my frame or not, it is what it is!! Clean or messy, stable or twitchy, "masterful work" is easy to spot, even if only their masters name that appears on the down tube. For example, Curt Goodrich builds for Rivendell, I think he takes great pride in his work, even though some Rivendell owners may never learn his name. That doesn't diminish his skill in my view.
I have as much reverence for classic marques as the next listee, but that worship is based on the product, not the name on the frame. In the end should it matter less if John Doe built that Masi, than the "master" himself? It doesn't to me.
Grant McLean
Toronto.Ca