The Eastern, Osceola, Merriam's, Rio Grande and Gould's are actually all sub-species aren't they. Isn't the Osceolated its own species? I'd have to look back at some Turkey Call's to be sure.

The grand slam is the 4 US birds Eastern, Osceola, Merriam's Rio Grande. Add the Gould's and you get a royal slam add the Oscelated and you get a World slam.