The difference between the black and green label is the time of "aging"
Black label age for 4 years, green label for aprox 2 years. No matter what the location in the warehouse. So you could say green label has less quality. But that's a personal thing.
Single barrel indeed comes from the "topfloors" of the warehouse as well as the Silver select.
Gentleman Jack is "charcoal mellowed" twice instead of one time which is the thing with the other Jack Daniels brands