Sounds like you have a wise vet. Too many start puppies too young with vaccinations and maternal antibodies interfere with them.
In one study of a cross section of different puppies the age at which they were able to respond to a vaccine and develop protection covered a wide period of time. At six weeks of age, 25% of the puppies could be immunized. At 9 weeks of age, 40% of the puppies were able to respond to the vaccine. The number increased to 60% by 16 weeks, and by 18 weeks of age, 95% of the puppies could be immunized. Parvovirus: Serious Diarrhea in Puppies & Dogs
It's always advisable to wait two weeks after that last vaccination for full immunity, which it sounds like you've done.