Allow users to select from only two available styles
 

I want to limit my users to be able to select from two styles only. I went into style manager and made sure that only those two styles had the check box selected next to them. The users were able to select from the one of the styles I selected and all substyles under it. The other style which has a check box next to it was at the top level and doesn't appear to be selectable at all. What am I doing wrong?