There's probably some mixing of Osceolas and Easterns along the border where they occur. I've seen 2-3 birds from S Louisiana/Miss border area that hade some very "Osceola" looking primary wing feathers. I have shot a Rio Grande with a fan that is indistuinguishable from an Eastern, and another that looks an awful lot like a Merriam's.

Turkey coloration varies withing some defined norms. Along the borders between two different subspecies, or in the presence of feral birds, hybridization will occur. For example, Easterns from PA and KS compared side by side may look very different.

In an attempt to keep the records of Grand Slams as clean as possible, the NWTF will not recognize a bird as an Osceola unless it's taken from a county, below a line from just south of the NE corner of the state running something like 45deg to the Gulf of Mexico.