Guess this stamp of a Sturmabteilung could be genuine after all

SA. der NSDAP.

Standarte J 21

Weißenfels, Klosterstraße 8

Sturmabteilung der Nationalsozialistische Deutsche Arbeiterpartei

Standarte J[ägerstandarte] 21

Weißenfels, Klosterstraße 8

     See Daniel Siemens, Stormtroopers:  a new history of Hitler's Brownshirts (New Haven:  Yale University Press, 2018), 336:  "Although the SA suffered severely from the drafting of the majority of its more than one million members into the Wehrmacht beginning in the autumn of 1939, the organization continued to provide a multitude of services to the regime until 1945."  Etc.