Unfortunately, Jentz in Panzer Tracts fails in giving a date of peculiar improvements, but from captions of photos it may be concluded, that in fall of 1943 Alkett Stugs already had it (and Alkett StuH received improvements at the same time).
BTW: Jentz claims, that it was actually named Topfblende (pot mantlet), and Saukopf was invented in a postwar literature
