The concept of “true value” is incoherent, at least in my model of reality. The correct price to attach to a good at any time is its market price at that time. If you had the set of information I listed in my last comment, you’d have the market prices, since they’re implied by the other stuff.
It might be valuable to talk about a “true value” of a given good to a given agent. Yes, the correct price to buy or sell a good at is always the market price; but whether I want to sell at that price or buy at that price depends on how much I want the good. If I sell, then the “true value” of the good to me is less than the current market price; and if I buy, then the “true value” of the good to me is greater than the current market price. In general, the “true value” of a given good to a given agent is the price such that, if the market were trading at that price, that agent would be indifferent regarding whether to buy or sell that good.
It might be valuable to talk about a “true value” of a given good to a given agent. Yes, the correct price to buy or sell a good at is always the market price; but whether I want to sell at that price or buy at that price depends on how much I want the good. If I sell, then the “true value” of the good to me is less than the current market price; and if I buy, then the “true value” of the good to me is greater than the current market price. In general, the “true value” of a given good to a given agent is the price such that, if the market were trading at that price, that agent would be indifferent regarding whether to buy or sell that good.
Yes that is a coherent definition of true value. It’s not a concept that maps well to price indices though.