USERRA amounts

Box 12 has special reporting instructions related to the Uniformed Services Employment and Reemployment Act (USERRA). If there are any elective deferrals, salary reduction amounts or non-elective contributions to a pension plan during the year are makeup amounts under USERRA for a prior year, you must specify the prior year contributions separately.
Note:  The contribution applicable to the current year does not require a year designation.
On the W-2, report the year (beginning with the earliest year), the code and the amount. For example, elective deferrals under USERRA to a section 401(k) are reported in Box 12 as follows:
Code Year Amount
401k 2013 2000.00
401k 2014 2406.50
401k 2015 1002.50