The Ones We Leave Behind - S1-E12
Revealing mistake: When Matt is running across the rooftops doing Parkour to keep up with the car he's following, there is a shot of him running towards another roof about to jump. In this shot, it's clear there is a stunt double in Charlie Cox's place. (00:29:27)

Revealing mistake: When Ellison shows Karen the article detailing the Central Park massacre, a close-up of the newspaper is shown. Next to the article headlined "Central War" is another article that appears to just be incoherent rambling. The text also appears to have been repeated numerous times as well. (00:32:58)
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.