Are the peacocks in the pics (Dad and Son) examples of birds with one or two copies of the White-Eye gene? Deerman was describing birds with one copy as having only a few white ocelli, while birds with two copies have most or all of the ocelli white. Based on that, it looks like the father has only one copy of the White-Eye gene. What about your bird's mother? If she also had one (or two) copies of the White-Eye gene, then it's possible that your bird has two copies, which might explain the extension of white in the train.
If the father has a white throat patch and white flights, then (based on what others are saying) he's Dark Pied. That means that his son has inherited one copy of the Pied gene from his dad. What most people call "Pied" (heterozygous for Pied and White) is not the same as "Dark Pied" (homozygous for Pied), so even if the breeder wasn't raising "Pied" birds, he could have some Dark Pied birds in his flock. Perhaps he presumed that those white markings on the throat and flights were simply further effects of the White-Eyed gene, when in reality, they are indications of the birds being homozygous for the Pied gene.
Is the father also Black-Shouldered? If so, does the breeder have pics of him when he was the same age as your bird? I'm still wondering if the extra white is a remnant of juvenile BS plumage. In your pics, the white flecks continue along the back toward the train. I wonder if next year your bird won't have this extra white in the train because by then he'll have lost the last traces of his juvenile BS plumage. Otherwise, I'd presume it's an effect of the variability of the dual expression of the White-Eyed and Pied genes over the effect of a new mutation.
