That makes more sense, thank you! Though do gold assets on the books really never get adjusted? I guess that's up the central bank to decide but I would find it surprising.

It's the rules of how they must account for the value of the gold they have. Gold is valued at the price paid. Then, it is valued at the price sold. If there is no sale for more than a century, it stays on the books at the price paid. Once a transaction happens, the numbers update. Then, the gain that everyone knows is there is 'realized'. It's like if you mined Bitcoin in the early days. Your gain is only 'realized' when you actually sell it. Until then, it is only theoretical.

Mark-to-market accounting systems are one way to deal with this quirk, but they create their own issues.