I am no eastern expert (so I changed the title so a few might chime in) But my understanding is that at the edges of the ranges of these species there is some natural integration.
The reason I would say brooksi or floridana is that the basic body shape and pattern of these species is kind of like an eastern except the black areas are very faded and mottled. Your snake shows just a little bit of this. Maybe a 75% eastern? Its imposible to ever know for sure. The best you can do is guess, and not market offspring as pure easterns. Asking for pics of the parents could clarify things quite a bit as well.
Another reason is it is also an extremely likely hybrid. IE the same people tend to keep both species and they interbreed very easily.
Very pretty snake though. Great orange coloration still showing.