Dear Aaron,
Its finding subletter because it has the same key as Albany. It was probably changed.
One question, do you really need to select several localities? a dropdown field would be so much simpler.
Anyway, I think you can try unchecking the option to store "0" when the checkbox is unselected. This will give you the option to update pre-existing values.
Please let me know if you are satisfied with my answer and if I can help you with any other questions you might have.
Regards,
Caridad