Return Text or Data Validation List

So, it translates like this?

=IFERROR(INDEX(Range_to_Reference,AGGREGATE(smallest,ignoring_errors,(ROW(range_of_rows)-1)/(Within_RANGE-Greater_or_Less_Than"",ROW(From_rows-1to1))),"")

Just to make sure I'm following.

Also:
D18 Should be equivalent to something to the effect of

=IF(OR($D$10="","OptSelect"),INDIRECT("OptSelect"),$D$10)

Where the Cells
D19,D20,D21 would be something like

=IF($D$18="OptSelect","",INDIRECT($D$18))

I am sorry this is such a pain.