They are simply units of an accounting system

The stuff in the basement of the Fed. They are units of an accounting system and their job is to move those units in and out of the economy.  They need that pile of ink and paper, in the basement, to count money not in the economy. The fiat banker operates the first differential, their pile are units of flow, and they come in and out of the basement. Otherwise they are like any other normal manufacturing business.

 If by law Congress is required to go into the basement and take all of the Fed inventory, then it is a nearly hopeless task for the Fed to keep track of their business. Imagine if the shareholders of General Motors monthly went to the factory and removed all of the aluminum stock. General Motors would be forever tracking down aluminum in the open market for instant delivery.

 I would expect Congress to overdraw their seigniorage, and I thought that is what we meant by the term. But evidently, all of the Fed inventory in the basement is classified as earnings to Congress. I never would have imagined something this stupid would have become law.