It is not until people are committed - I am only circumspect with information if I do not know the people enquiring. I prefer people to get in touch long before any breeding takes place, I can then ascertain if they are suitable and the breed is suitable for them. I would provide info such as any sire/dam is fully hip/elbow and eye tested as per the KC/BVA schemes.
I expect the possible owners to visit to meet the breed and ask any questions, it also works the other way and I can ask them questions.
If I know I am planning to breed and I am happy with the people interested I will then provide further information and copies of all the relevant information. I have no problem with them confirming everything with the KC online.
Purchasing is a 2 way process, the possible owner have to be happy with all aspects of the planned mating, in turn I have to be happy with the possible owners.
It is very sensible for possible to check all the information, on the other side though breeders have to be careful as to how much detailed information is given out. As I posted earlier unfortunatley there are people who are not quite as they seem, before you know it pups of the same breed are advertised with the names of dogs, particularly the sire, on the online selling websites.
Thankfully I breed very rarely, only when I will keep a pup for myself, I normally have people already on a waiting list and do not ever need to advertise, so the situation of having to provide information to complete strangers does not happen.
I believe you can provide enough information to satisfy a "cold" enquiry in order to open the dialogue. If for some prospective owners that is not enough, that is fine - each party has to be happy with the entire process.
The details of dogs are available in show and working catalogues - some of the enquiries can be started by a person calling saying "I was at XX event and I really liked your dog NN, do you plan to have any puppies from him/her in the future?" My response could be, no sorry his/her hip score is a little higher than I would like so I will not be breeding for them, I do however have a younger dog who if he passes all his health tests I may allow him to sire a litter, if that is of interest to you why don't you come a visit to meet the dogs". I would not expect to provide any further pedigree information on the dog until I have met the possible owners. Demanding to see his pedigree at that point (unless someone was known to me) would make me wary.