The Missouri instructions actually do give you the option to either file as a full year resident and claim the credit or as a nonresident. They don't really provide the option to specifically file as a part-year resident.
I'm including the link to the instructions for your reference as well. As you scroll down in the link, you will see in the Part-Year Resident instructions, it says "a part-year resident is treated as a nonresident but may determine his tax as if a resident for the entire year". This just happens to be one of the states that can treat you as a nonresident even though you were technically a part-year resident.
Missouri filing for part-year resident instructions
I am happy you were able to get it sorted out so your income is not being taxed when it isn't taxable in Missouri.
**Say "Thanks" by clicking the thumb icon in a post
**Mark the post that answers your question by clicking on "Mark as Best Answer"
