I must be stupid, but I only just realised that the scores in the club challenges were *cumulative*, at least for drift events. One of the drift events I was sure my club wasn't doing so well in came second, and I see it's because it wasn't just me who entered, but Gen X as well and our scores accrued.
Fuck, wish I'd known this before!
Fake edit: Wait, I think in the club challenges, it shows two different things: The total points earned per team, and the team with the winning time/drift points. So the team who finishes #1 with points may well not win the challenge if the #1 driver was solo in team B but team A had 6 entrants.