Shipley or Cumbernauld

I've just received details for a new PAYE scheme, but although there is an accounts office reference, it does not say if this is Shipley or Cumbernauld. I guess I have to wait for the Yellow pay booklet to find out which one. Which set me pondering: why do they maintain this distinction, given that all post goes to Bradford anyway, and two separate bank accounts. I am assuming that there is no duplication of references so why not dispose of this now apparently artificial split?