Once you have an identity protection pin assigned to you, you must use your IP pin every year that you file a tax return (for the rest of your life, as far as we know). The IRS will mail a new IP pin each year to your address on file, so if you move during the year, make sure you inform the IRS of your change of address.
If you don’t receive or lose the IP pin, you can’t e-file. If you file by mail, there is a place next to your signature to write in your IP pin. If you leave it blank, processing your return will be delayed so the IRS can verify your identity.
You may be able to retrieve your current year IP pin online, although this may depend on whether or not you have previously set up a verified account with the IRS.
https://www.irs.gov/identity-theft-fraud-scams/retrieve-your-ip-pin
