Being for sale = having a price. If there is no price, it's not for sale. If it's not for sale, there is no price.
The value of an asset must be marked for many reasons, such as when it is used as collateral for a loan, for tax purposes, or just to see if what valuation benchmarks are being hit. So if you are getting a mortgage on a house, the bank needs to mark is value, even though no sale is happening.
What you are describing would be mark to limit. I have a limit order set on my puts of $186, even though the current market price is $2.57. The limit order is the price I would be willing to sell the asset, without knowing anything else. So if I sleep through a huge rise in prices, at $186, I do not believe they will go that much higher that I would be able to delay selling them with the possibility of losing out. I could just as easily set the price at a trillion dollars each. If we used mark to limit, then I would able to claim to be the richest man on earth.
Or put another way, imagine you have a house that as a realistic value of $100k. You live there, so would not sell at $100k, but would demand a premium to move out of a house you love. Then you start thinking, and say you will sell the house for a billion dollars. If the bank used mark to limit, they would loan you $500 million on that house that now has a value of a billion dollars.