When did the Luger magazine hold open variations begin?

Howdy Y'all
When did the Luger begin using the magazine hold open function?

1913.

Must've been a leisurely transition as my A series 1914 DWM lacks this feature but does have the attachment lug for the butt stock.

Those already issued were sent back at a later date and wrere usually marked accordingly.

Thanks Y'all
I'm doing research on the P08 series and there seems to be a mix and match information stream.
I've seen the hold open function as well as the sear bar cover talked about but no definitive answer on when they first appeared.

The order to begin manufacturing the P.08 with the hold open was issued in May of 1913, and the sear bar change was adopted about February of 1916. The stock lug was added to military production beginning in 1913 with the adoption of the LP.08 (Artillery).