Yes, you have it exactly right. File part-year resident returns for Iowa and Maryland. You want to report your income earned while you lived in Iowa to Iowa and then report that income again when Maryland asks for non-Maryland income.
The wages from your two states in Box 16 should add up to Box 1, or at least be very close. Sometimes states tax things a little differently than federally, so the total might be slightly off, which will probably be due to an item reported in Box 12 of your W-2, like life insurance policies above $50,000. If the two box 16 amounts are significantly higher than the Box 1 total and it does not look like it's attributable to something reported in Box 12, it is possible you are being double-taxed on a portion of your income, maybe for the month of the move. If that is the case, you should receive a tax credit in Maryland by reporting that you were already taxed on it by Iowa.
