Nested IF formula not evaluating correctly

I have the following formula in a cell

=iferror(if('Plant Master List'!$I9="Don't","Don't",
            if(search(",1S,",'Plant Master List'!$I9)>0,"SS",
            if(search(",1G,",'Plant Master List'!$I9)>0,"GG",
            if(search(",1T,",'Plant Master List'!$I9)>0,"TT",
            "Nooooo!")))))

If the cell in 'Plant Master List' contains Don't or ,1S, the formula works, but if ,1G, or ,1T, are in the cell it doesn't return anything.

I'm expecting Don't or SS or GG or TT, but I am only seeing Don't or SS

What have I missed?