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)
Character mistake: When Matt is talking to his priest Father Lantom, he says "it was a nice sermon" instead of "it was a nice homily." In the Catholic church "homily" is the correct word; sermons are Protestant. (00:11:30)
Continuity mistake: When the Punisher knocks out Daredevil he wakes up with a gun taped to his right hand. When the Punisher says that Daredevil has to shoot him, Dardevil struggles to escape from his chains and we get a shot from his right side, where the gun is no longer there. In a later scene it returns. (00:32:05 - 00:34:55)
The Dark at the End of the Tunnel - S2-E12
Visible crew/equipment: When Frank closes the door to the shed, you can see a crew member in the trees to the right swaying left to right as if he were looking for something. (00:45:15)
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)
Seven Minutes in Heaven - S2-E9
Continuity mistake: After Frank stabs Dutton in his jail cell and Dutton falls to the floor, Frank's white prison uniform is clean, but when Frank exits the jail cell there is blood on the collar of his uniform. (00:40:05)
Continuity mistake: When Frank Castle walks up to Murdock, the chains are wrapped around his torso, two over his chest and three over his abdomen, but when the shot cuts, it's one over his chest and four over his abdomen. (00:17:40)
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)
A Cold Day in Hell's Kitchen - S2-E13
Continuity mistake: Before the last fight there are over 30 ninjas waiting for Daredevil and Elektra. Elektra kills like 5 or 6 of them and Matt struggles just with Nobu, but when the fight is over the rest of the ninjas are dead below the water tank.
Seven Minutes in Heaven - S2-E9
Continuity mistake: The wound on Fisk's right cheek changes length and position during the whole chapter.
Continuity mistake: While Matt and Karen are talking outside of the courthouse, the sun changes between shots.
Continuity mistake: The bruises on Castle's face are dark then faded and then dark again.
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.