Just a general observation/comment, but apparently some were numbered outside the orbit of the established depots, probably by organic or mobile armorer teams. I have several rifles that have had numbers added, sometimes on parts not numbered in original production. There are many French rifles and carbines done like that, and one of my Carcanos has had numbers added.
The presence of depot stamps on otherwise new looking rifles is definitely strange, but was probably normal at the time. Were they selected at random as 'representative samples?' Who knows, but there are obviously some with no modifications or even minor changes that have depot stamps for some reason.
I think you're correct about the depots doing a formal inventory of seized Italian arms, as period sources note just under 400,000 Italian rifles and carbines in inventory by December 1943.
