It reminds me of a joke about Japanese due diligence. It never ends until the boss says "enough!" Having said that, I guess it's a matter of degree. In this case one of the challenges is that the seller is a shop that usually sells much more conventional and less antique watches. So although they will initially claim that they stand behind authenticity guarantees, when pressed I suspect they will say "caveat emptor" which to me is no guarantee at all. As they say, "buy the seller" so I will probably pass on this one, nonetheless I will go and study and admire this watch more while I have the opportunity. Thanks again all for your guidance and kindness.