I'll edit the year in your question title. See DoninGA's comment above that addresses your issue.
Expanding on that a bit, if you have the Self-Select PIN from 2015 (the one where you chose the 5 digits), then it can be used again for 2016. If you are referring to an assigned efile PIN from the IRS in 2015, it cannot be used again. If you don't have the chosen Self-Select PIN, you can choose to verify in the AGI field instead. You can use the 2015 AGI from an original 2015 return, not an amended one.
