You can find the CP or LTR number on the right corner of the letter. This notice explains how the increase in tax was calculated and how you can challenge it in the.I know folks here probably get tired of these posts, but I have a letter showing in Informed Delivery from Austin, Tx in a rather plain envelope An IRS Verification of Non-filing Letter provides proof that the IRS has no record of a filed Form 1040, 1040A, or 1040EZ for the year you requested. This letter is a self-correcting letter. The goal is to have you, as the taxpayer, self-correct. We sent you previous notices asking that you file your tax return.