Visible crew/equipment: Wesley enters Vladimir's office to talk with him and Vladimir had a large white window behind him. As they talk, the reflection of a green screen of these windows is in Wesley's glasses. (00:06:34)
Continuity mistake: When the paramedic examines Foggy he places the stethoscope around his neck with the chest piece hanging to his left, but when it cuts to the view from inside the ambulance the stethoscope's suddenly hanging around his neck the opposite way. (00:17:30)
Continuity mistake: When Matt and Foggy are talking with Nadeem after he testifies, in some shots, Matt is holding onto the top of his cane, but in other shots, his hand is further down. (00:39:35)
Continuity mistake: When Karen, Matt and Foggy are in Matt's office discussing, Karen looks over at Foggy and has her hair raked back over and behind her ear. When it cuts to a close up of her, she now has a lock of hair down over her cheek. (00:17:15)
Continuity mistake: After Matt and Claire kiss, she says she wondered when he would do that. In that shot, he has both of his hands up on her shoulders, and she is holding one of her own hands against her chest. It then cuts to a side view and now only he has one hand on her, further down her arm and her hand is down. (00:05:07)
Rabbit in a Snow Storm - S1-E3
Continuity mistake: Turk is showing off a pistol at the start of the episode to John before buying it. Before he says the gun will not jam, he is pointing it to his left, but when he says his name in the angle change, it's pointed to the right. (00:02:00)
Continuity mistake: After Foggy shows Matt the plaque for their office names, Foggy is speaking to him and his hair is over his ear. It cuts to a closer angle and suddenly he has his hair raked behind his ear. (00:30:54)
Continuity mistake: Matt is talking to Sgt. Brett who sets down a pen on his desk. After Brett starts to get up and lifts up his cup, the pen is still on his paper. When the camera cuts to an over the shoulder view from Brett, the pen vanishes. (00:21:53)
Continuity mistake: Foggy is on the phone with Mat, telling him about some people and he wishes he was blind. There are other pedestrians walking behind him in this shot. When it cuts to a close up, the people behind him suddenly disappear.
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.