What I find interesting is the way the numbers have been applied,each individually vs in a block. If they were field applied they would be haloed from the stress on the metal being pushed aside,much like early lugers that had numbers and proofs applied after finishing, one of the first thing professional collectors look for.
It is rather odd...
Buxton's volume II offers some great info on spreewerke,i and he notes most of the knowledge is "rudimentary" because the Russian steam roller ate up any records that may have been left.
I always liked how they varied in tones and finish.where some could be well finished and others crude and all business!