Query about Aoshima 1/70-scale kit

I have just acquired Aoshima’s 1/700-scale kit of the Balao Class submarine.
The box actually contains components to build two models, each with the option
of full hull and waterline. Something that puzzled me, a separate sprue containing
parts for a different type of conning tower, and labelled ‘Tree USS Submarine (16-03)’.
The instructions highlight these as ‘not for use’. Is it that the various boats of the Balao
Class had different conning towers? The one I am modelling is USS Bergall (SS-320).