If N Nested formula

This is my current formula:
=IFERROR(VLOOKUP($B6,Codes!$A:$K,MATCH($A$4,Codes!$A$1:$K$1,0),0),"")

I need to add another level to it. I have added a column & if it has a N in the corresponding cell, then I need the cell where the above formula is located to pull from another column than originally planned.

Make sense?
INS WorksheetORIGINAL.xlsx