Well, my limb is starting to crack! Jes found this thread on Jan Still's forum:
http://www.gunboards.com/luger/topic.asp?TOPIC_ID=4652 reporting 1920 DWM #5335. This also refers to #4134n in Jan's Weimar Lugers, p. 140.
Ross Murchison reported 1920 DWM #7138n in the latest Auto Mag.
I have queried my database and come up with quite a few more. Adding those from replies in Jan Still's forum results in the following list. With the exception of #2977n, all have police unit marks and/or sear safeties but this is probably skewed by my database containing only police unit marked examples. These include police units in Prussia, Saxony and Thuringia.
1699n (and b)
3108n
3176n
4605n
4134n
4647n
5335n
6655n
6938n
7138n
9483n
From the range of numbers it looks like there were 10,000 of these produced. Any more out there?