The Erfurt parts will have been replacements, likely when the pistol was modified for police use.

Erfurt was an Imperial Arsenal while DWM was a privately owned company. Every part on an original Erfurt Luger will be stamped with a crown/letter somewhere. It's easy to see on your side plate. Even the grip screws were stamped by Erfurt on the early Lugers but that practice stopped about 1915. Every other part was fair game.

As an Imperial Arsenal, Erfurt was obligated to follow military directives such as the 1916 instruction to notch the front of all receivers for the rear sight of an Artillery model even if the pistol was made with the 4 inch barrel. Erfurt did but DWM as a private concern didn't have to and didn't.

Nothing wrong with having a "shooter" as your first Luger. Mine had 98% of the original finish with a shiny bore. It was put together from 4 different WWII pistol's made before 1940 on the 1936 frame.

Paid $300.00 for it back in 1988 and still shoot it a few times a year!