[DonVoigt]

Please post more pictures of your pistol and all markings.
Looking at one mark out of context can be misleading.

That is an Eagle/33, one of the Simson inspector markings; though it does look like a
"6" slipped in between the "threes" somehow.

It is an inspection or acceptance marking not a "proof".

Simson made parts and pistols and repaired pistols(lugers) throughout the 1920s and into the 1930s; New production was dated only in 1925 and 1926(few in '25 and even fewer in '26).
Most Simson production was not dated on the chamber at all.

Many Simson made barrels were sold to and used by the police in rebarreling their pistols, the barrels themselves will have the last digit of the date on the bottom;
a 3,4,5, perhaps a for the corresponding year 1923-6. Maybe a couple others but all the barrels seem to have been made or marked at least in the early '20s.