The 2016 1099-R and payment that was paid in 2016 (whether received and cashed or not) is 2016 income that should have been reported on a 2016 tax return. Being "sent a check" is constructive receipt. Moving without informing the employer, post office, IRS and others of the address change is the taxpayer fault and is not an excuse.
The 3 year statute of limitations for receiving a 2016 refund has expired, but the clock for failing to report taxable income runs for 7 (and sometimes 10) years. I additional 2016 tax was due then the interest on that unpaid tax started on April 15, 2017 and increases each month until paid.
There is a good chance that the unreported income would have no change in the tax due depending on all other 2016 tax information.
TurboTax no longer supports 2016 - you might need a tax professional to amend 2016.
**Disclaimer: This post is for discussion purposes only and is NOT tax advice. The author takes no responsibility for the accuracy of any information in this post.**
