It's not your job to figure out how your employer should file, just how you should file. You have what your employer plans to give you. What you have to do is decide how to report it on your taxes. 1) Don't include the D17 in the D code entry, as this will generate an error. Instead code it as other. 2) If the contribution lowers your taxable income as declared on the W2, then all is well. Better to just accept that than to go back and refile 2017. It probably doesn't, though, so you want to go back and amend 2017, lowering your taxable income in view of the 2017 contribution made and reported in 2018. If you don't want to call a CPA, who might have to just do research with your employer and pay stubs anyway, try first calling your person at your employer, whom you've probably already talked to and ask for help on how to report it. They'll probably help you. (Of course, you're still responsible.)
