In Derived column you use following expression:

(@[User::CopyofLT] == "B1") ? "STD" : ((@[User::CopyofLT] == "B7") ? "Q2FC" : ((@[User::CopyofLT] == "B8") ? "Q3FC" : ((@[User::CopyofLT] == "B9") ? "Q4FC" : "NonSTD")))

I have used a variable to test the expression, you can replace it with your column name. This is working as you described for all cases.