Thise stormtroopers at that point in time would also have been leftover clones as well as imperial trained troops. A lot of people think palpatine would of had them destroyed but that wouldnt make sense strategically as the clones were commissioned by syphadeus (sideous) to be completely obediant to palpatine. To destroy them would make absolutely no sense but to use them makes a sound strategic army. Why destroy an army to create a new one when yiu can have your army and make it bigger