In the Blood - S1-E4
Continuity mistake: Karen is talking to Urich in a diner as he is drinking from a mug. As she is saying there has to be a trail, the camera is behind Urich and pointing at him fiddling with his cup. In this shot, he places his thumb over the rim of the cup down inside it. Then in the next shot from over Karen's shoulder, suddenly he is just holding the cup normally. (00:12:24)
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.