It seems that a "machine translation" from a Russian site is not any clearer than one from a German site.
Ger,
The proof marks I see are from the period 1891-1939.The DDR adopted very similar marks, causing your confusion. The DDR used other marks that are entirely different than the 1891-1939 ones. These marks are not on the gun in question. One of these is the date stamp. DDR guns were dated, but Suhl proofed guns were not dated at the time the guns serial number indicates it was made. I believe a DDR gun would have a 70mm(2 3/4") chamber. The 12 in a circle indicates this gun has a short chamber, which is consistent with a Prussian gun. Like the others, I believe this is a proper Prussian gun.
Gunwolf
I noticed that difference also, but it looked like an 18 to me. The bore of both tubes was marked 13/1, which is common for 12ga guns.
Mike

Last edited by Der Ami; 04/21/16 12:37 PM.