
As they titre tested for Rabies after a month and Scandinavian countries wanted 120 days from vaccine to titre, then I think you'd be fine with anything along those lines.
I would think maternal antibody interference is more likely than vaccine failure.
http://brettwinn.hubpages.com/hub/The-Truth-About-Dog-Vaccinations"A puppy is typically given a series of "puppy shots" that begins as early as six weeks of age and concludes around sixteen weeks, followed by a "booster" at around one year. These vaccinations are wasted when the puppy is still protected by the immunity he received from his mother. Maternal antibody interference is the most common cause of vaccine failure. Exactly when the immunity conferred by the mother wears off varies between puppies, but it is known to last longer than previously thought. Up to twenty percent of 18 week old puppies have enough maternal antibodies present to interfere with successful Parvo immunization. One option is to delay vaccinating entirely until the puppy is over 22 weeks of age. Delayed vaccination undoubtedly reduces the risk of VAAEs, but requires vigilance on the part of the puppy's owner to be aware of disease risk and to make intelligent choices when exposing his puppy. The time period prior to such delayed vaccination overlaps one critical to socialization, so it is important the puppy be socialized only in places where the other dogs are known to have been immunized, such as friends' homes, and not public places such as Pet Smart where the status of dogs encountered is unknown. Certainly the beginning of a vaccination series should wait until the puppy is at least eight weeks old and longer when possible. Allow a minimum of three weeks between vaccinations."
The latest 2011 US and Canadian protocols advise, that the final vaccine should be administered after 16 weeks.
https://www.aahanet.org/PublicDocuments/CanineVaccineGuidelines.pdfNow I really don't think American and Canadian dogs have different immune systems to ours.