The confusion with FN Mauser models originated with the 1930s FN Catalogs, which often showed the 24/30 nomenclature. This was done as customers could select either model, as both models were available in the early 1930s.
This nomenclature should never be used today in order to identify rifles as customers did either select a 24 or a 30 model. There is no such model as a 24/30 as there is no hybrid between the two. There are distinct differences between the 1922, 1924, and 1930 models.