So, while collecting evidence from the Crimson Caravan and Silver Rush, the second piece of evidence doesn't trigger the next stage of the quest. I assume it's because I already looted the Silver Rush's safe after killing everyone. I've got the note that you need to continue, so I think I'd be alright if I could advance the quest using console commands (sqs, setstage). The only problem is that I don't know the quest's base id. It hasn't been listed on the Wiki yet, either.

If anyone knows what it is, could you post it? Or, alternately, tell me how to find it?

Use getstage 15DA16. Then use setstage 15DA16 .

(Should be 50 for get so you should need to set to 60 as far as I can tell.)

Is this mission a mission from the Crimson Caravan? I just started with them and am curious as to if it reaches this mission you are referring to from the one I currently have about Cass and the Gun Runners and stuff.

Yeah, it's the last part of Cass' mission. Spoiler in the next line, fyi.

Mucking about in the console didn't work for me. I could only compelete the mission via setstage; I couldn't just advance one objective. And completing the mission by the console didn't give Cass her bonus perk. So I gave up and shot McLafferty in the back of the head with a silenced pistol so I wouldn't lose NCR rep. Quest complete.