What, aside from tests and traceroutes documenting "specific services are slow and others aren't", would be evidence of throttling?

Asked and answered, situations like the Comcast/Bittorrent one works.

How do you know CS has no knowledge of it? If it's company policy, they would probably know.

No, they wouldn't, and if they did, you're now alleging a massive conspiracy where no Verizon CS agent has ever not toed the company line.