You are correct, accidents happen even with responsible breeders, but that doesn't mean that health testing of those pups should be any different than a pure bred litter. Mix breeds can have eye problems just as much as pure breds.
That is correct, those mixed pups got the exact same treatment as our purebloods, and the buyers, got the complete Basenji handbook that I had put together years and years ago. And you are correct any dog, pure or mixed, needs to be vetted yearly.