Did you notice that this plate number has a letter "F" in front of the numbers? That is not typical. I understand that the "F" was applied only on one top corner of a plate and it was added after the plate was inspected, accepted and then surface hardened for use; thus, indicating the plate was"finished". That makes this stamp position more identifiable and a bit more rare than any of the other plate number positions on the press sheet. Thought that was worth sharing - Good Luck!
Thank you for that information.....This stamp was originally part of a plate of 6 and the perfs separated....so now I have a block of four and two singles.....