Maybe I can clarify a little bit for you...
The name blackmouth is nothing more than a nickname that has been given to the fish from Puget Sound anglers- simply becasue of the lining of the gums and tongue. The name will carry from California to Alaska.
The Canadians refer their fish to Springers because of the spring stock returning to the rivers in the local area.
The name is no different than calling Chum- dog salmon or a large Chinook a Tyee.
The only way to identify a blackmouth from an adult is by cutting the fish open. If there is an egg skein or milt sack it would be classified as an adult fish or Chinook. If there is niether, the fish would be classified as an immature chinook or juvenile chinook- aptly nicknamed a blackmouth.
Since a high majority of our returning fish are of fall stock, one could easliy identy a springer when cleaned... if there are eggs or a milt sack in April, May or early June, you have caught a springer!
Hope this helps.