To add to this, some spending is done in chunks for the year or doled out every month.

Some money may be given back to the government if it isn’t spent.

Some money is purposefully cryptic in its spending for national security reasons.

There are a lot of things that make it difficult to accurately track things against the entire government, which is why auditing individual departments/agencies is how it’s usually done. However, even then it should be better than it is.