I have uploaded a couple of other examples of holdopen retrofits from a 1911 DWM and a 1912 DWM for reference purposes. See below.
If your frame and receiver serial numbers match, then you probably have a 1913 DWM made before the changeover order in late 1913 which required stock lugs on all subsequent Army Lugers.
Both my 1913 DWMs have integrated holdopens, consistent with "Imperial Lugers" tables, and I cannot explain the presence of the retrofit on your 1913.
Perhaps someone else can comment on this.
Luke
