The presence of only two acceptance/proof marks on the receiver indicate it was a "spare" receiver and perhaps not used or assembled until after the 1920 marking (which lasted only about a year from 1920-21, though only 1920 was the property marking applied).
The "Su25" seen on the bottom of the barrel, also indicates a replacement barrel, assembled/used when built/rebuilt at the Spandau arsenal ca. the late 1920's.
The numbered right grip is likely the original grip, the left grip was often replaced - especially if the pistol received the magazine safety during "upgrades" in the 1930's. The mag safety was later removed or inactivated as they caused function problems, but the grip which was cut specifically for the mag safety was often retained, or replaced with another grip at the time.
A picture of the upper grip area with the left grip off would help, as would a picture of the inside of the left grip in total or just the upper half.
The spare mag is the #2 mag from another police luger.
Don't worry too much about the over strikes, they may simply indicate use of a previously numbered part during the extensive rebuilt that this pistol received; it was likely refinished during the 1930s update, and appears to be original to work done in that period.
I'm not sure what you mean by "squibbling" and 100 years, but it has been 100 years since this piece was first made, so maybe that answers the question- in the future- who knows.
