Most of these have the Initials E.D. on rear which is common, I have always believed this was a PB employee, but I have
a new lot of material and while the majority of proofs in this lot are marked E.D. there are also R.D and I.D. So I am now thinking the second letter D might be for DIE? And the first letter E, I, R may be types of dies????
Does anyone know what these initials actually are? I am just guessing!