FYI, I finished this job and the number of coax cables coming back to the closet was absurd. We only made half of them live (one for each room), but that was still something like 13 cables that we terminated into two 8-way blocks. We brought the main feed into a three-way block, with one connection for the router and the other two for each of the 8-ways, and it all seemed to work just fine. I still think there should have been two ethernet and one coax at each spot, but whatever.

When I actually got on location I saw what the problem was. Clearly, an electrician ran these low voltage lines. He ran every one of them to a full electrical box. This made it very hard to deal with slack, though fortunately (and weirdly) he made them all two-gang boxes. That helped with the cable slack, but it was very weird in the end to see all these double-gang wall plates with just two coax connectors on one side and a single ethernet jack on the other. I have a couple dozen 3-port keystone single gang wall plates in my garage that we could have used if the electrician had just run these to single-gang low voltage boxes.

Anyway, we got the job done and the client is happy. They'll never, ever use those 13 coax cables, but they have them!