I only know a little about this one. For fairly modern guns, each maker has a code assigned to them. Arietta (and Grulla, Ugartechea, AyA, etc.)each use a sequence of numbers beginning with their unique number. Arrieta is 57, so 57-03-12-97 is (I believe) the 3rd gun completed in the 12th month of 1997. (Can anybody take this back to the earlier stuff?)
The post-war period had a little experiment in socialism that caused all the makers to be lumped under one giant consortium, DIARM. This was an unmitigated disaster that blemished the reputation of all their guns for quite a while. I believe that the DIARM stuff was in the 60s & early 70s, but I'm not very solid on that. By the middle 1980s, things had returned to the more traditional English master/apprentice system and better quality returned to their guns. The makers I mentioned above, (plus a few others) make some really good guns that are an eceptional value in a hand-made firearm.
