Current Playthrough, I couldn't finish the Raiders at GMS, and didn't know that I could just ignore them.
Went to Junkyard to buy components for a vest, killed elwood, raided his place, etc.
Now I come back, and I get a quest to get the card from Elwood.
Well, turns out he's dead, and the card vanished when I used it on his door.
Or I don't have it for some other reason.
That kinda blocks a quest line.