SVRR archives has two plates off of different engines associated with SVRy. In the one case the boiler with it's smoke box and plates still attached had been used in stationary service and our organization acquired the boiler. In the other instance the plate was removed from an engine also in a legitimate manner. Clearly some were removed in the dark of night and I know of one of these that involves what is today a famous engine sporting a replacement plate. However as Martin says the large number of engines going to scrap reduced the practical value of most of the plates to nothing more than scrap value or what collectors were willing to pay. Even if the plates were stolen off of engines in scrap lines, a plates values at the time was a dollar or two at most as scrap bronze, and this petty theft surely not worth calling the cops for. Yes it was stealing, but in the big picture, no one is is going to track down the perpetrator who stole a plate in the 1950's off of an engine that is now part of a Toyota bumper.