City is not in geographies hierarchy and zip code belongs to multiple cities.

Summary:

I have a situation where a zip code is shared between multiple cities. I can manage tax calculation properly, but when trying to enter the legal address for these parties, it doesn't exist in the geographies, as would be expected, because of the scenario. To make it clearer, hopefully, I would need to be able to enter an address as Chesterfield, MO 63017 or Town and Country, MO 63017. These are both in the same county. I have the exact same situation in another state and county with multiple cities having the same zip code. These are small towns.

My questions are as follows on the related Geographies: