I've seen enough funny stuff come out of Mauser, so an unnumbered, unproofed M1914 doesn't really surprise me.
These were also made as tool room examples, sales examples for use in advertisements and manuals, etc... But it also wouldn't surprise me if one of the Mauser workers built one for himself
Of course, one would need detailed photos to establish if the markings were removed or were never there.
I have an unnumbered HSc as a cutaway, as well as an unnumbered and unproofed Mauser Parabellum here.