The white hackle throat is just a recent discovery. I believe there are only one or two written references to it in publications (Bates isnt one of them). If you're interested in further reading, you can check this blog post by Don Bastian
I'm sure (obviously by your fish with the GG suck in their lips) that the white hackle throat is not deciding factor for fish to take them. I merely mentioned it as a bit of an aside to the pattern. Whats also funny is that Hilyard book on Carrie Stevens also doesnt list the throat, but the photos of the GG in the book have the throat- i have the book and just checked!