In your original question you stated "I filed as full resident Iowa and part time Missouri state tax returns..."
Did MO explain why they changed your MO income percentage?
Did your MO employer mistakenly withhold MO taxes after your move to IA?
I would respond to the MO Adjustment Notice by advising them that you relocated to Iowa and became a domiciliary resident of IA on such-and-such a date (the date would be the date you began living in your new home in Iowa), and that the MO percentage of your income is based on the portion of your income that was earned while you were still a MO resident. If they ask for proof of your Iowa residency, I would submit a copy of your lease if you're renting, and a copy of one or two utility bills. An Iowa drivers license isn't good proof, because people often wait for months after a move to obtain a new license. But they can't wait months to pay their electricity bill.
**Answers are correct to the best of my ability but do not constitute tax or legal advice.
