Machining variations and front sights.
 

Went through my collection, here's what I found.

RB=Rounded Back FB= Flat Back

1900 DWM AE -RB, Blank

1900 DWM Swiss -RB, Blank

1906 DWM Swiss -FB, Blank

1906 DWM AE -FB, Blank

1906 DWM AE -RB, Illegible

1906 DWM Comm. -FB, Blank

1908 DWM Comm. -RB, "J"

1911 DWM Army -RB, "O"

1912 Erfurt Army -RB, Blank

1913 Erfurt Army -FB, Blank

1914 Erfurt Art. -RB, Blank

1915 DWM Army -FB, "D"

1916 DWM Art. -FB, Blank

1917 DWM Art. -FB, Blank

1917 DWM Army -FB, "N"

1917 Erfurt -FB, Blank

1918 Erfurt Police-FB, "O"

1920 DWM Comm -RB, "G"

1920 DWM Police -RB, "8"

1921 DWM Police -FB, "1"

1921 DWM Police -FB, "1"

1923 DWM Comm. -FB, Blank

1936 S/42 -RB, Blank

1937 S/42 -RB, Blank

1939 42 -RB, Blank

1940 42 -RB, Blank

1940 42 -RB, Blank

1941 byf -RB, Blank

1942 Banner -RB, E/N