So, if I have an Erfurt without proof marks and no date but only the serial number on he left side is either forced matched reciever or buffed so much that all marks disapeared.
Where there any commercial Erfurt Lugers?
Alf

Erfurt was a MILITARY production arsenal... no commercial production.

Lugers confiscated after the Great War (WW1) that were of Erfurt manufacture, may have been introduced into the commercial market, like much war booty was... but no commercial guns came out of Erfurt.