Is anything in box 12?    If the employer contributed to the plan in 2016 (even if it carried from 2015) then it applies to 2016.  If you think the W-2 is wrong, contact the employer for a corrected W-2.

Thanks very much. No, there's nothing in block 12. I'll contact my former employer and assess filing an amended return.

The employer might still have contributed to the plan even if you did not because of the severance pay so you would still be covered.  That would not show up in box 12.

My termination letter dtd 10/2/15 states specifically that participation in benefits based on employment status (e.g. Cash Retirement Income Plan, Savings Investment Plan (401k), Long-Term Disability, etc.) will cease as of the date your employee status ceases.  Health insurance benefits extended to the end of the month in which severance ended.  The Cash plan (company money only) would have continued to pay interest but there were no further contributions after Oct15.  Same for the SIP/401k (employee money only).  Thanks very much for your responses, by the way - very helpful to consider.