Probably some admiral's discretion. I'm serious, I think something like this is probably an arbitrary decision from a higher-up at Starfleet HQ. Otherwise, the Peregrine could easily have just been another Constitution-class with some minor differences.So what makes a certain type of ship a completely different class, and what makes it a variant of the same class?
 
				 
 
		 
 
		 
 
		 
 
		

 
 
		 
 
		 
	 
 
		 
 
		 
 
		 
 
		 
 
		 
 
		 
 
		 
 
		 
 
		 
 
		