The fact is that Sweetgrass (b1b1 cgcg dd EE NN RR SlSl SpSp PnPn) have more in common in their color genetics with a Royal palm (b1b1 cgcg dd EE nn RR SlSl SpSp PnPn) than they have with a Tiger Bronze (b1b1 Ccg dd EE NN RR SLSl SpSp pnpn).
If I cross a Sweetgrass tom with a Royal Palm hen, the female offspring will be Sweetgrass phenotypically and genotypically. The male offspring will be Sweetgrass phenotypically but genotypically they will be carrying a recessive Narragansett color gene. By your theory the Royal palms would be a Sweetgrass variety which they are not.
Just because you use Sweetgrass to create a different variety, it does not make the other variety a Sweetgrass.
On
Porter's Rare Heritage Turkeys, he does not make any claim that the
Tiger Bronze is a Sweetgrass variety.
Since I don't allow Facebook to run on my computers, you will never see me in the
Facebook Turkey Color Genetics group.