“And that is probably why the U.S.’s statutory price of gold stays fixed at a decades-old level of $42.22. The consensus that independent central banking is a good thing (because it keeps a lid on inflation) dictates that the Fed have plenty of ammo. If the official gold price stays at $42.22, the Fed can lay claim to the full 261,498,927 ounces held by the Treasury. If the price is increased, the Fed gets only a sliver of that, the Treasury laying claim to the rest. And with fewer resources, the Fed’s has less control over the purchasing power of currency.”
It's not so much about 'ammunition': for that it doesn't matter how the central bank accounts for their gold.
The archaic official value of gold is just a political left-over from when the US was part of the Bretton Woods system, and no politician has found it advantageous to change that relict.
Just like we are still labouring under lots of other old regulations. Like taking our shoes off at the airport.
tldr; the Fed owns gold certificates which give it a claim on a $11 billion worth of gold held by the US Treasury. They don't have a claim on a number of ounces of gold, so the US hasn't changed the convertibility value of gold certificates of $42.22 set in 1973 so that the Fed's claim on an absolute mass of gold remains unchanged.
It still doesn't quite make sense to me, because if the official value matched the market value, the Fed would still have the same claim to their book value of gold. It makes me think that something else is going on that's intentionally obscured.