if you are due refunds for any year from 2012 through 2015. it is forfeited. if you owe the IRS can come after you forever.
many pro's keep earlier year software and they could prepare 2012-2015 returns if yu owe or you can download the forms from the IRS website
https://www.irs.gov/forms-pubs/prior-year
if you live in a state with an income tax, the state's website is the best place to start to get the forms if you are going to prepare those returns
