I see many breeders give a 1 year health guarantee for congenital problems. I assume HD falls under the same guarantee. Since the dog has to be 24 months before you can get it OFA certified, is a 12 month guarantee enough? Do HD issues arise before the 12 month guarantee expires? I have seen some breeders give a 24 month guarantee for HD (in a different breed that I'm interested in). I think 24 months is more appropriate....any thoughts? Thanks.