4th Data validation dependent

[Endorphin]

Hi all,
I am trying to get a fourth data validation column in this contextures document, does anybody have any idea on how to go about this.

I know there are other ways to do 4 column dependant data validation but the format this uses allows for easier additions to the data.

Any help as always is much appreciated.

http://www.contextures.com/DataValMgrProdClass.zip