Kasztelan - you are quite right.
Spoiler
The StuG is from 10 Pz.Granadier Div., left behind close to Frydek-Mistek in May 1945.
It's a standard summer 1944 production by Alkett, just the Shürzen plates and the loader's MG shield have been fabricated in the field. These StuGs were assembled with a newly designed roof layout, including an opening for the Rundumfeuer-MG. However, this option was available in extremely limited quantities, until the production was finally improved by October 1944. Since no loader's MG shield was fitted, the troops quite often built their own.
Also, the factory issued Shürzen plates came with a poorly designed mounting system - so many field workshops had to improvise and customize the plates (this eventually led to the factory made 'swinging' Shürzen). StuG III Ausf. G had only 30mm of side armour, that could be penetrated by a 14.5mm AT-rifle (tests were conducted on Panther Ausf. D - the 14.5mm could also fully penetrate the 40mm lower hull side of Panther Ausf. D.). I hope this help!
Refers: Müller: Sturmgeschütz III Vol 2, Panzer Tracts No. 8 and 4-3