KC registration isn't a guarantee of a well bred, well reared litter. Nor a guarantee against falling into the hands of puppy farmers.
These days, registration is not even a guarantee you're getting a pup with the lineage claimed on its papers - ask the people who've DNA tested their KC registered cocker spaniels and found they have a sprocker!
And not every unregistered litter is poorly bred from non-health tested parents with no regard to temperament or working ability or improving the breed, or from dodgy puppy farmers who are over-breeding and not registering the 'extra' litters.
I had a family member who bred, competed in confirmation showing and judged KC shows for his breed. He got so fed up with the KC's inaction on health issues and welfare that he flounced and refused to register any subsequent litters. He and his dogs were amazing. He's no longer with us, but when he was, he bred infrequently and interviewed [grilled and cross examined] prospective buyers with care when planning litters, and he had the puppies' backs for life. Registered or not.
I currently have, shock horror, a non-KC registered working line cocker spaniel. I don't want to compete in working tests, or breed, so it makes no difference to me. I wanted a healthy dog with a reasonable but not ridiculous working drive and a nice temperament for living as part of the family. That's what I got. In am ideal world , e'd have been KC registered as well but in the scheme of things, that weighed less with me than all the boxes that WERE ticked by his litter: both parents were fully health tested clear and hip and elbow scored; I knew the dam and two of her previous litter and liked their temperaments; I knew her owners so could be 100% sure I was buying from genuine people who breed occasionally to keep a puppy and that they would care for the litter well; I had seen the (KC registered) sire work and liked him.
However, the breeder was straight with me re lack of papers for the dam and therefore the puppies. The alarm bell for me re KC registration in the OP is being told one thing, and that then not happening.