Skeetx: Yes, I can see the reproof code front of left barrel flat but where are seeing the original proof code? There were no Birmingham proof codes until the 1920's and London didn't introduce them until 1972. Are you mistaking the Birmingham View and Definitive proof marks for date code stamps? These were discontinued in 1904, the Diamond with the nominal Chamber size introduced in 1887 so the best you are going to get from the original proof marks is 1887-1904.
I see quite a few old 12b shotguns with tubes proofed at 14. These tend to be at the cheaper end of the quality range but that is not a hard rule. I have always assumed that this may have been a way of saving a few pennies: one can use a smaller tube blank if one bores a smaller hole up it AND get good thick walls. Probably a majority of the Birmingham gun trade were producing guns down to a price, not up to a standard, so every penny counted.
