I was perusing the Scott Classic Specialized Catalogue and noticed Scott lists German stamps used in Austria after the 1938 annexation. I was sorting German stamps at the time, and discovered these three.
The first stamp was postmarked in Vienna at some time after annexation (the date is unreadable, and the stamp is heavily creased). It is listed as Austria Scott A485.
The second stamp was also postmarked in Vienna, in March 1943. It does not have an Austria Scott number because it was issued after 1940 (the Scott Classic Specialized Catalogue goes up to 1940 only).
The third stamp I really don't know. The postmark reads "THERESIEN...O...". I don't know if the location is associated with Theresienstadt / Terezin in occupied Czechoslovakia, or some other location. If anybody can decipher the town name and location, I'd greatly appreciate it.
If you get a chance, post images of your German stamps used in Austria after the annexation.