While the pincers may have linked up, was the encirclement that strong around the Sixth Army that it couldn't break out early on? I remember reading somewhere that Soviets were stunned by how many troops they had actually encircled, and had to send additional troops to reinforce the perimeter.
I will try to at least add something to what the Soviet forces blocking 6th army were. There would be two perimeters. One facing 6th army and one facing the actual Soviet German front that 6th army would have to break through to free themselves over what is a long way, many many km.
On the Nov 24, 57th and 64th were definitely on the perimeter facing 6th army.
On Nov 26, 21st army was definitely on the perimeter.
The reason for example a breakout was possible for the Red Army at Smolensk was because follow on forces were not in position, and there was not stable perimeter.
Not to mention at some point in the breakout attempt, I think they are basically assured to come up against Soviet tanks to which their only real counter is artillery, something they were possibly lacking and something they might even need to leave behind in order to escape if they can somehow escape the perimeter facing them.
The Red Army entrapment of 6th army was one of the greatest deep shock strikes in the history of war, over a vast lateral expanse engulfing the 6th army, it had the terrible foreboding of Cannae.
Edited.