My 1099-R was issued in 2017 with a code P for 2016 since it was issued before the 4/18/17 tax deadline for 2016 taxes but TurboTax only lists code P as taxable in 2015.

I believe the software is incorrect in assuming the 1099-R could have only been issued in 2016 for 2016 taxes. It could have been issued before 4/18/17 to apply to 2106 taxes. Please advise on how to proceed.