I am told that the Smithsonian has the record book(s) that provides the cross reference between the complex serial number that would show in the specification books and the builder plate numbers.
I have seen a 1902 letter from the BLW to H.M. Yerington (of the V&T) regarding new cylinder casting for the ng 2-6-0 that was owned at that time by Inyo Development Co. He wrote giving the builder plate number and the then current name. Baldwin responded that they showed that plate number being on an engine delivered to Eureka & Palisades. They provided the complex serial number and asked that he check that that was the number stamped at several locations on the running gear and other locations.
Brian Norden