Multi-select fields with INDEX and MATCH (Multiple value output)

Hello fellow Smartsheet users!

I am trying to do something I THINK is unique, but don't know IF it is possible. I am building an intake/work/request management tool for my Marketing department at a global company. My Finance department through me a curve ball, and wants accounting information attached to certain requests.

My Finance Team need the following on the applicable requests:

Cost Center (Essentially a Sales Channel for the sake of this post)

Account Number

Region

I was 100% able to have it identify what requests needs it, and based on criteria and nested IF formulas define Cost Center and Account Number. The Region is the tricky one.

The requester is able to multi-select values for where the asset being requested is essentially going to be used. They want Region in the accounting to be contingent on what value(s) are selected for asset destination.

Here's the tricky part, this is not a 1-1 match. So I can't just INDEX/MATCH against a reference table. They want to know if two (or more) options are selected what Region they fall in without duplication of the Region in the output, and that if they cross regional bounds, and they want the output to list all applicable regions without again without duplicates.

See example table here:

Right now, I'm using the following formula in the Output column.

=IFERROR(INDEX([Index Col]:[Index Col], MATCH(Input@row, [Match Col]:[Match Col], 0)), "Multi-Regional Request")

Ideally, the expectation being that "City 1" and "City 2" are selected in row one so the output would be "Region 1" and "Region 2" in the Output.

Row two is working fine, obviously only one value is selected.

Row three has "City 2" and "City 3" selected, so the current expectation is that Output populate with only one instance of "Region 2".

ANY guidance here would be greatly appreciated!!!!