graf, hopefully a "rewrite" of areas won't occur, as Graham and I should have found you sooner!
(and I don't think there are errors, but as things are learned...)
The E/67 and E/81 only appear in the "a" suffix, Unless we come up with specific dates of a pistol with a marking, we guessed a date of around 1932 - 1934 for the "a" suffix. Don Maus is working on police guns and spcifically a Simson or two that has police markings and this might help nail down some dates.
As you also said, as we find other collectors of diverse Simson items, the date also might be nailed down closer. One thing I was curious was that the Simson firm made machineguns, and yet the few collectors I talked too had never seen E/6 or E/33 on the guns. Yet, it would make sense they did so... Unless the rifles, machineguns, etc were accepted by another inspector, thus did not get E6 or E33 (or the like).
Ed