Is that the earliest that they could have been used? Or did the Ansi standards just codified what was already common? Graflax supposedly still offered it's older style back up to the 1950's. Almost bought one of the SLRs but decided the combination of the holder issues and the min focal lens of 190mm was too much of a tradeoff.
I guess I should just stick to something from the 1960's or newer but the more choices the better.