Hi as a breeder this is what i do and i havent had any problems.
Normally at 7 weeks of age i send of the application form to the KC, i wait this length of time to ensure that all the pupies are healthy and ready to go to new homes.
The new owner is issued with the pedigree certificate which gives the details of mum and dad, date of birth, colour and sex, along with other relevant info that i think new puppy owners should have.
I explain that the paperwork will be sent as soon as it returns from the KC and normally i have not had to wait longer than 6weeks for the paperwork to come throu, in fact i would say that these days 4 weeks is about the norm. As soon as i recieve the paperwork it is then forwarded to the new owners and i follow this up with a telephone call to check that they have recieved the paperwork and it also gives me a chance to see if the puppy has settled in as well.
Hope this helps you, if you havent recieved it by 6 weeks after getting your puppy i would give a quick phone call to the breeder, it doesnt do any harm and you did buy a puppy in good faith as KC registered.
Bye Chris