M36, M40, M43, some M44 and some units like Panzer Lehr were wearing Assault wraps for the infantry. Basically any combat uniform of the war. Hell, in the Netherlands, you even see some Reichswehr and modified Dutch tunics popping up. The Germans reissued everything, and some companies simply never stopped making the earlier models. One should remember that no tunic was ever phased out officially, they just wore out. The German army updated the look of the tunic in order to make things easier on manufacturers, but there was NEVER an order to change uniforms or even to force manufacturers to produce a specific model if they didn't have to/want to. This goes for all German uniform parts- many things considered 'early war' were still being produced into 1944 and 1945, including M36 and M40 helmets, pony packs, etc.
M43 and M40 tunics WOULD have been most common by 1944, but there were plenty of guys still being issued or wearing their original M36 tunics.