Just keep in mind that often those white tail feathers (and sometimes in the wing hidden in the fold) don't come in until the Cocks are a year old, or two or three. I find most of the feather(s) that get white are only partially white and only the occasional full length white feather. Do check the underfluff of your birds, I find in mine, the white feathers have correlated with gray/white underfluff on the rest of the birds body. Underfluff should be black. Honestly, I don't quite know what to think of it all other than this is a challenging breed!!