Questions to Ron Wood - Hold open catch

[Darth 44]

Hi !
Ron, in the thread "Navy mags" (Navy Lugers forum) you wrote:
"Presumably as a cost cutting measures, the Army elected to eliminate the stock lug that the Navy had adapted, the grip safety, and the hold open.
Until the LP08 came along, there was no need for the stock lug, so that was a logical choice for elimination. The grip safety was actually redundant (cavalry troops might argue to the contrary) so it too met a well-deserved demise as a military necessity. However, not knowing when your weapon was empty in a heated disagreement proved to be an embarassment of significant proportion. So in 1913 sanity reared its head and the hold open was once again recognized for its vital role and returned to its rightful place in the military Luger,where it remained to the end."

So, am I correct assuming that after 1913 there were two variants of the P08 in use?
The older variant without the hold open (let`s call it pre-`13)and the then new post-`13? If so, have the pre-`13 P08s been successively upgraded by manufacturer/s to the post-`13 hold open standard,or such a rebuild was/is impossible and all hold open equipped P08 Lugers had to be built from scratch?

Regards.