Data Validation (List) too long

I am trying to create a drop down list that see's the entry to left of it and brings down the appropriate list.
My code is as follows:

=IF(A2="1 BCT",FBCTBNS,IF(A2="2 BCT",SBCTBNS,IF(A2="3 BCT",TBCTBNS,IF(A2="4 BCT",FORTHBCTBNS,IF(A2="212 FIRES",TOTFIRESBNS,IF(A2="15 SUS",FIFTEENSUSBNS,IF(A2="11 ADA",EADABNS,IF(A2="402 FA",FOSFABNS,IF(A2="1 CAB",CABBNS,IF(A2="OTHER",OTHERBNS,""))))))))))

This works just fine.

However, I need to add more to the code as my list to pick from has gotten longer. My problem is that the code is too long.
I have read from other sources that one can put the code simply in the workbook and name it then reverence back to it.
This does not work for me as when I put the code in the sheet, without it trying to create a list, it doesn't make sense. So if I try to reference back to it in list, it returns #VALUE.

Is there any kind of work around that I can do to accomplish more characters to a drop list in data validation?