In the eyes of the tax man there are no mistakes. There are only audits and fraud. Better have your stuff in order when that audit rolls around anything more than a few pennies out of line and you'll be looking at months of extra work even if you're a small company. Looking back at a decade or so of your paperwork will turn up a ton more that you'll have serious issues documenting if you didn't take care of it at the time.

That gets expensive in a hurry (tax lawyer, fines, interest, surcharges).