Ah interesting. Birmingham Assay Office Info about hallmarks.
You will see there what you are missing from the set and one error.
It is as you say a great system and medieval in origin. Preventing debasement of the materials. Anyone can stamp a number on but the proper hallmarks are put on only after ‘assaying’ checking the metal is the standard said. It is a thorough nuisance and a cost but invaluable really.
My London set with the millennium commemorative add on. (minus maker’s mark)
Ah right it is all normal/bump faked. Effective though looks more like the modern option for laser etched versions.