Heard on a documentary that around Stalingrad, the Soviet leaders decided that after certain modifications, the T-34 was “complete”. What you got out of the factory was it. General Zuhkov stated that this was the tank to win the war.
This meant that each army group had the same standard. No more fooling round with “2nd generation” projects or “super weapons”. The factories would simply crank them out like bread from a bakery. It also made logistics more manageable.
The two biggest modifications for its standardization were a radio in each tank (before then it was flags & hand signals...only unit commanders had radios) and welding armor plates instead of rivets. Rivets had a nasty habit of breaking off upon shell impacts and ricocheting inside the crew compartment).
“The factories would simply crank them out like bread from a bakery.”
The factory was near Moscow and the soldiers would drive them out the factory door to the front while the castings were still warm!
Actually the T-34 design changed over the years, primarily with turret design. 1940 turret was rolled and welded steel. The 41/42 turret was cast steel with approximately the same shape and profile as the 1940 turret. The 42/43 turrets were cast steel slightly higher and with a little more room the 41 turret. The late 42/43 turret had a commanders coupla added to the turret roof. From mid 43 on, the turret was enlarged to carry a 3 man crew and the 85 mm gun. The turret race for the 85mm gun turret was the same size as the 76mm turret, so a lot of the earlier 76mm gun T-34s were re-turreted with 85mm gun design. While the turrets and guns were changed often, the automotives remained pretty much the same with the same 500 hp diesel engine as the 1940 version used throughout the war.