Left receiver bears only the last two digits of the serial number. To the extreme right is what looks like a Simson-style eagle (no pendant) under which is Za(illegible)t.another depot marking.
The left-most stamp (crown over T) is overstamped with an eagle of horizontal wing depiction, no pendant, under which is HZaJt3 which I have now learned was a Berlin depot responsible for storage, issue and repair. It appears to be left to right crown over T, crown over S, crown of S etcetera. The right receiver has the normal German military receiver proofs of 1914-1918.
The four-digit serial number is 10XX with no suffix letter. All numbers match, including internal small parts, except for a WWII magazine, and grips. I have a 9mm 1917/1920 DWM and have been photographically recording markings and looking them up.
