> According to standard economic theory though, the fact that someone says "I'm worth $X to them" is completely irrelevant and, because the transaction never happened, never becomes data.

I don't understand that. If an employer offers $X, I'd say that means the applicant was worth at least that much to the employer, assuming the job offer was legitimate. I suspect it's fairly rare to get an offer for $X, only to find out that the employer was lying and won't actually pay that much.