Yeah, but remember, he had a number of different stud dogs, of different types of collie, and collie hybrids too.
I would think in the early days he experimented on those different studs, and the various lines of greyhound, with the best intentions. He had a reputation to earn for this venture to be a business.
But Plummer's fixation with the merle coloured dogs, and subsequent book promotions, took him to think not of working ability, just sales...
His book, My Life with Lurchers gives some insight as to the various types he was producing.
That said, I believe those dogs