In those past years, the statute of limitations for refund purposes of an NOL, followed the 2016 statute of limitations. Thus, if an NOL from 2016 was carried back into 2014, and was filed timely before April 15, 2019, a refund would be issued.
The question becomes:
1. I believe you have to carryback the NOL to 2014 and 2015, as the time period to waive the carryback has expired.
2. This should have been filed by April 15, 2020. The statute of limitations for 2016 expired on April 15, 2020 (in general; certain exceptions may exist, but generally in favor of IRS, such as audit adjustments 3 years from the date the original return was filed).
3. If you have not filed the amended return for 2016 by April 15, 2020, if the NOL from 2016 is large enough, you should do the computations to compute the 2016 NOL;
then compute what happens if carried back to 2014 and 2015...and if there is some NOL leftover, than you could carry that remaining amount forward to 2017
Here is a link to Pub 536 for 2016 for further information and help.
**Disclaimer: Effort has been made to offer correct information; but due to the discussion forum limitations, the poster disclaims any legal responsibility for the accuracy of the poster's response**
