> It's still embarassing for the country, though, because for such a person, the government already has all the information on the form and already has all the money, so really the government should send the form to the taxpayer instead of the other way around.
I'm pretty sure that they do do those computations, and if they don't match the ones on the form that the taxpayer sent in, they send a letter saying "you did it wrong, here's the correct answer, we'll just use that unless you argue".
In fact, a few years ago my filing got lost in the mail or something, and in the process of re-submitting I discovered I didn't have back-up copies of some of the documents like W-2's that *must* be included in the filing. It turns out that the solution to this problem is, you call up the IRS and they print out a copy, mail it to you, and then you mail it back.