I have looked at this site before and it is my studied opinion that these guns were not engraved by LDN, despite the signature.
Roger,is that Colt policy to prevent someone from I.D.ing an engraver and trying to commission them to moonlight?Or maybe hire them away from Colt?
mike
Other American engravers did sign their work in the 19th century, particularly John Ulrich and Gustave Young.