well really this is down to unscrupulous (sp) restorers who wont disclose these things when they sell on.... i myself have a portfolio everything is documented that has been restored / re made etc etc.
if they are to be stamped Ben could i ask that it is on the hidden face as you state...after all if i was lucky enough to get my carrier in a movie i am sure it would spoil the historic appearance of the vehicle if it had BEN 2011 stamped into the face of the cast