With tax litigation the issue is that you have to prove you didn't simply shift money and accounting briefs around, and the only way to realistically prove it is to show all the statements in the time period that you'd required to keep them (I think that's the last 6 years).

The government basically comes to you and says they think you owe X, and you have to prove that false to their satisfaction. The more data you give your CPA to work with, the better.