[DonVoigt]

My opinion was that the tooling for the addition of the hold open was used in 1913-1914 and not after at Erfurt; perhaps not ever sent to Simson. All pistols "requiring" hold opens had them by 1914.

There is much discussion in one of the books about the addition of the hold open to pistols originally made without it. I'll find the right book and pages - likely in Goertz and Sturgess- and add the reference for those who want to read more.

I know of no special modifications required for Reichsheer service; other than the requirement for shorter barrels to meet IMKK dictat.
Whether adding a hold open was a big deal or not, it would not have been necessary- with thousands of pistols being destroyed- why would anyone choose to upgrade or rework a pistol without a hold open?

Anyone with more info is welcome to chime in.

I found the reference in Goertz and Sturgess "Pistole Parabellum" pp 1099 to 1105, in the red edition, and 1056 to 1066 in the green edition.
Sturgess writes that the installation of the hold open was a "major factory retrofit" requiring milling of the recess, placement of the pivot pin, fitting of the hold open itself, and then function firing of the weapon. It was also decided to add a higher front sight at the time of function firing to correct the higher impact point of the early sight, the effect of the sight change was to reduce the point blank range to 50 m from about 100 m.