Hello,
Paolo is a collector who did show that some 1930 stocks are numbered, that all you can read in the following topic of J.C. Stills forum of Okt.2003
http://www.gunboards.com/luger/topic.asp?TOPIC_ID=507
I think too, that it is not too unusual to have a unnumbered stock.
I have several of them, 2 1930 stocks and one which I belive is a Bolo Stock, with the Mauser logo on the side.
all of them are not numbered.
The very early stocks i have seen however are numbered with the full serial numbers!!! They are milled out in a little bit different kind ( the bottom where the magazine is, is flat and not rounded like in the more modern ones for example.