Hello Rick
It all depends on what the requirements are. Remember that subnetting is something that you end up applying to a real world network so the network range you start off with can be anything. If you are given a network of 192.168.0.0/23 and you are asked to further subnet it to segments of /26 then that is what you will do. There is no rule that says you must start with a /16 or /24. Now if you are told to specifically come up with classful result, then this means that the resulting subnets must be classful. So if you are originally given the 192.168.0.0/23 range then the resulting subnets you create must have a /24 subnet mask.
I hope this has been helpful!
Laz