Resurrection - S3-E1
Continuity mistake: When Matt is recovering in the orphanage, his bandages around his torso keep changing position. They go from just barely below his nipples, to covering them completely, to way below them in the same scene.
The Ones We Leave Behind - S1-E12
Character mistake: After Gao and two of her men walk by in the warehouse, Matt jumps down at attacks one of the guys. The other guy is behind with a sub machine gun in his hands. While he was walking it he carried it partly pointed down to the ground like normal. Once the other guy was jumped, he begins to fire, but the actor continues to point the gun down at the floor like this shooting the ground no where near anybody. He only starts to raise it once Matt get's close to look like he gets hit. (00:40:01)
Other mistake: When Matt and Claire are on the roof and Matt says "A dead guy, a guy I witnessed burn to death," Charlie Cox's natural English accent slips through. (00:41:35)
Chosen answer: After some research, I can say that no, Cass is not a character of Marvel, nor is he present in the Netflix show. As far as I can tell, it's either a real person, or a random name chosen for the coffin, most likely the former. In another season of Daredevil, the show utilized a real cemetery displaying real names in the tombstones.