Sorry, I have moved several times in the last year and I cannot find my campagnolo catalogs CD.

As for the material, if two expert frame builders have told you they are certain than I guess you could just roll with that. Based on the components it does appear to be from before 1995 but that is not conclusive. I don't think straight blade forks became en vogue till the later half of the 1990s so I would still question that date. But 531 and 531R were still being used in the early 1990s and there are examples of 531 straight blade forks so it they think it is 531, I would believe them.