Factual error: At an eating area, a collector shows a man a computer screen with his daughter in real time and has her call him. She then speaks in the phone and you can see her lips and actions lining up perfectly with the words he is hearing. It would not be this perfectly in sink even in the most optimal of conditions. There is a slight delay between the video from the camera and sending that to the computer being shown. And then there is also a slight delay of the phone single traveling through one phone to the other. These would not line up right and so the father would not see the lips moving exactly with what he hears his daughter saying over the phone.
Continuity mistake: When Karen is telling Mat and Foggy the story, and mentions that things got blurry like she was drugged, she is making gestures with her hand. Between shots, the position of her hand changes from one spot to another. (00:27:30)
Continuity mistake: When the debt collector is talking to the man in the park eating area, there is a cup on the table in front of them with a straw sticking up, but leaning to one side. Each time the camera cuts to a different angle and even coming back to the same angles, the straw is always changing positions pointing in different directions. (00:19:36)
Continuity mistake: Foggy meets Brett at a subway and begins talking. He says they have been enemies since they were four but not to blame it on career choices. Between shots, Foggy's hand goes from down at his side to suddenly on his own chest. (00:09:58)
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.