Very early post war Sauers were made in the old factory in Suhl. The Sauer trademark had moved to Eckernforde(?) by the time the pictured gun was made( note the proof house "house mark". After the move, there was all new machinery and all new designs. New parts didn't work with prewar guns and the model numbers didn't match the new model names. After the move, Fortuna was made on the old machinery.
Mike