Other mistake: In the scene where Janice is trying on her wedding gown with Carmela, her tattoo is gone. However, in all the other shots, her tattoo is ABOVE her cleavage line between her boobs. It's nowhere to be seen in the wedding dress shots.
Revealing mistake: While Christopher and Furia are dismembering Richie Aprile on a meat saw, you can see that the blade of the saw is still, but the blood is splattering all over the place and you can hear the sound of the meat saw cutting through flesh. (00:49:55)