I dont think this means what the tweet implies.
Book value is what is paid for an item (less depreciation if applicable).
Replacement cost is usually higher than book value due to inflation, etc
it would be like giving your nephew the broken down Chevy Silverado you paid 20,000 for but is 20 years old and currently on your books as zero because its fully depreciated but you tried to convince the family what a generous person you are because you gave the kid a $50,000 (replacement value) Silverado when in all likelihood, you just gave the kid a hunk of metal and a problem
As I understand it, the US is giving Ukraine old equipment so when they do that it has to be removed from the governments books with an entry equal to the amount of the book value. If they use a higher replacement value, it would result in a negative value for the equipment on the books (which should be pretty obvious the minute they make the entry).
So for example, if the total book value of the equipment sent to Ukraine was 10 billion but the replacement value is 16.2 billion, this would result in an over valuation of the equipment on the books of 6.2 billion as well as an overstatement of the value of equipment given to Ukraine.
Its merely an accounting entry mistake and not actual cash..
YET..I'm sure they will now give the 6.2 billion to Ukraine in the form of cash or more equipment.
However it doesnt make a difference in the scheme of things if the total authorization was say 50 billion, that number hasn't changed because all of the above comes out of the 50B one way of the other
The problem appears to be that we agreed to fund Ukraine in the first place and didnt negotiate peace at the beginning when there was an opportunity to do so