Display Form Unique Values for ListBox

I have a Display Form with two List Boxes. ListBox1 is using a unique list as input data to populate it. ListBox2 is derived from the user's pick from ListBox1 using the cascading ID.

My issue is that the values in ListBox2 are NOT unique. There are 19 records, but only 3 are actually unique, though ListBox2 shows all 19. Is there a way to make these items unique/distinct? The REST endpoint has a "Return Distinct Values" toggle, which I clearly cannot utilize in my where clause within my ListBox2 Query Details.

Also, can someone verify that Runtime commands for the Forms do not behave like on-click events? In other words, whatever is in the Runtime commands will shape how the form behaves when the client first sees it. Additionally, I would LOVE some examples of how to use these:

form.Find(Of ListBoxFormItem)("<FormItemID>").QueryLayerSource

 

form.Find(Of ListBoxFormItem)("<FormItemID>").QueryServiceUrl

 

form.Find(Of ListBoxFormItem)("<FormItemID>").QueryWhereClause

I hope that's not too much to cram into one post,

Ryan