Not sure how I feel about Manny as one of the 3 CB to be honest. But then again, he is pretty versatile, so who knows.
I don't think they were playing 3 CBs though.
They were playing "3 at the back" with Siggy on the right, Durra in the middle, and Manny on the left.
When the opponents pushed down their left (our right), Siggy moved to be the second CB next to Durra and Gulley tracked back to RB, and there were 4 at the back. Unless Siggy could field it on his own, in which case he would and we'd continue.
When the opponents pushed down their right (our left), Manny moved to be the second CB next to Durra and Doyle tracked back to LB, and there were 4 at the back. Unless Manny could field it on his own, in which case he would and we'd continue.
Th result of which was Manny was not playing as a CB except in exceptiuonal (rare) covering circumstances.
The only time we had 3 CBs was if the opponents were pressing down both wings simultaneously - in which case both Gulley and Doyle tracked back and both Siggy and Manny shuffled inwards.