> 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.
The only data point that matters is the one where you got hired and started receiving paychecks, all others are not factors at all.