Quite a few P08s with Schupo police markings from Hesse (
H.P.) and the city of Weisbaden (
S.W.II.) have been reported with professionally-removed stock lugs have been reported (HWIS, Chapters 8 and 16,
http://www.historywritinsteel.com/New_Insights.html, Item 11). Both of these areas were occupied by French forces following WWI. While I know of no documentary evidence of the reason for this, it is likely that the French required this removal to prevent the pistols being used as carbines.
If your pistol has either of these police markings and/or has the lug professionally removed, it is likely this is the explanation. A photo of the removal would be helpful.