As far as lack of Zimmerit goes, Sturmtigers were built from damaged tanks recovered on the battlefield. Lots of earlier production Tiger l’s lacked Zimmerit and when damaged ones were returned for conversion to Sturmtiger, Zimmerit was not applied. Zimmerit was out of favor, anyway, when this work was done. Any mid - to late- Tigers retained any Zimmerit they already had. Therefore, there is a variety of Sturmtigers, of different production schedules, with, or without Zimmerit, and with different styles of gun barrel, and differing superstructure details. Good info here: 38 cm RW61 auf Sturmmörser Tiger ‘Sturmtiger’ - Tank Encyclopedia
