Citi can't legally make spurious dollars appear on their Balance Sheet. They need to ask the fed to do it for them (...and I agree that the two are pretty close to the same thing lately).
The fed does get audited by one of the big 4, and the findings pubished; on and of balance sheetitems are included.
I think by definition the fed can't be undercapitalized. It'd like saying "you have too little of the stuff that you can create from nothing, on a whim, in whatever quantity you desire."