They will for the most basic personal deductions. I have gotten a correction on a 1040EZ where my deduction was corrected upwards and the refund increased. It is impossible for the IRS or your tax preparer to know things like what kind of automobile deductions you can take for your sole-proprietorship business. This is an impossible problem to solve - every change to the deductions allowed is going to make some people pay taxes on what should be business expenses/losses and/or allow other people to claim legal-but-bogus or just plain fraudulent deductions.