All tax documents must be entered with the year to which they were issued. If you need a duplicate 2016 1099, then you will want to contact the issuer.
If you filed a 2016 tax return, then you will want to amend it to include the 2016 1099.
However, if you didn't file a 2016 tax return and have previous year's tax documents that have not been filed, you still complete your tax returns. You can purchase desktop software from previous years
here.
You can find more information about completing a past tax return in the article
here.
