"Pure" is often over-emphasized as something singularly preferable. Of course, all things being equal, the purer they are the easier they are to work with, the more predictable, but chickens are extremely variable. I could take chicks from you, from one of your lines, and, introducing no new blood, have birds that differ from yours significantly in 5 to 10 seasons. The RIR gene pool is a huge gene pool in comparison to, say, the Dorking gene pool. I would take the variance you are witnessing--apparently all disciplined within the scope of their own strain--as a sign of vital biodiversity within the breed and a genetic acknowledgment that different breeders reading the same info interpret said info differently, and the effects of that different interpretation over a time-lapse of real-time selection leads to different strains with breed-representative variations. In short, one could read it as a good thing that they're not all identical.
From the point of view of one rather intimately acquainted with Don Nelson's stock, you have some good birds.