"...very low production / rare watch, and perhaps never sold in the United States so that our expert would not have seen or heard of it, or..."

Just my small contribution to one of Jeff's points above:

I think that the United States would have been in the past the obvious target market for an "Indy" chronograph, just as the current Formula 1 Indy LE is today, so it really sounds strange to me that OTD's resident expert in USA hasn't been aware of the existence of such a piece. I'm afraid that, unless some conclusive proof is shown, somebody will have a nicely executed fake in his/her hands.