You will have to ask your employer why the 19 is shown on box 12 with a D code.

D—Elective deferrals to a section 401(k) cash or deferred arrangement.
Also includes deferrals under a SIMPLE retirement account that is part
of a section 401(k) arrangement.

19 is for the year.  Sometimes they make a late contribution and would put 18.  

Ignore the 19 when you enter the W-2 information ... it is not required.