I believe that most if not all 'ethical' responsible breeders endorse. There are those who will not lift the endorsement under any circumstance which should be stated in the puppy contract. There are others that will lift the endorsement if certain criteria are met i.e reaching 2 yrs of age, having had all Health tests, being of sound temprement, having had some success at show level etc. etc.
Breeders are responsible for the pups they produce , endorsing them protects the pups, well in theory anyway because of course being endorsed for breeding means that any pups produced from an endorsed bitch or sire would not be able to be KC registered. However that doesn't stop them being bred from and pups being sold as non KC reg or registered with other non KC associations. Always stay away from non KC reg litters as they start the alarm bells ringing, if all is above board there is no reason why a litter would not be reg with the KC, though the 'breeders' come up with all sorts of lame excuses for not reg with KC.
As you appear to be looking for a pup I would advise you that those who endorse are responsible breeders
If you think you may have breeding plans in the future then discuss this with the breeder who will outline their criteria for lifting any endorsements (which is easy enough to do
) Good luck in your search.