Do I use 1099's labeled 2017 and 2016 for 2018 and 2017 tax filings ?"

[Carl]

No. income is reported only on a tax return for the specific year that income is received. For your 2017 tax return, you only use tax reporting documents that are clearly labeled as for 2017 only. If you use a 2016 form on a 2017 return, the return may be accepted, but you will be audited 24-36 months down the road after you file.

[KrisD · Accepted solution]

The forms dated 2016 are filed on your 2016 tax return, and this is done in the year 2017. This year, 2018, we are filing our 2017 tax year returns and using forms, like a 1099, labeled 2017. The 2017 tax return is due April 17th, 2017. 

The 2016 tax year return was due in 2017, but if you have not filed, and you need to, you should still file as soon as possible, although it will be considered late. If you owe for tax year 2016, you may be assessed a penalty and/or interest. If you are due a refund for 2016, filing late should not result in a fee.