This link has an excellent explanation of what registries are and why your cavalier should ONLY be registered with the AKC, the CKCSC, or a national club registry, NOT the bogus registries listed below (though note that even a proper club registration does NOT mean you are getting a pup from a good breeder, unfortunately... you need to research breeders carefully too!).
Kate of Noonvale Cavaliers put together this list of registries to watch out for. If you are offered a dog/puppy with one of these registrations rather than a national kennel club or breed club registration then you are talking to someone who is breeding or brokering backyard bred or puppy mill/puppy farm bred dogs. Committed breeders with quality dogs from recognised lines, and dedicated to both health and conformation in the breed, would simply never, ever need to register with one of these registries and would consider it a deceitful way of making a buyer believe the registration had some meaning and significance in terms of quality. It doesn't -- you can get registrations from any of these places by filling in a form and sending money, no matter what you are breeding and rergardless of whether it is even a recognised breed. With these registries, you don't even have any way of knowing if you are getting a purebred cavalier (but you'll sure be paying for one, at close to or the same price as a good breeder will charge). There's no verification process that the dog is purebred or from the pedigree stated.
Note that many of these bogus registries have the same initials of legitimate national breed clubs, in order to fool you into thinking they are proper registries.
I'd also add IKC= International Kennel Club, which mimics the legit Irish Kennel Club
Some puppy mill registries:
FIC - Federation of International Canines - mimics the legit FCI--Federacion Cinologica Internacional
CKC - Continental Kennel Club - mimics the legit Canadian Kennel Club
Canine Kennel Club
APR - American Pet Registry
North American Purebred Dog Registry
Krystle Kennel Club
Dog Registry of America
American Canine Association, Inc.
American Purebred Registry
America's Pet Registry Inc
National Kennel Club
Purebred Canine International Registry Service
United All Breed Registry
Universal Kennel Club - mimics the legit United Kennel Club
US Breeder's Registry
World Wide Kennel Club
Federation of Rare Breeds
National Pet Breeders Association
United American Kennel Club
United Kennel Club International
US Kennel Club