Hi there,
If I understand correctly, this will mean you get a new rabies jab about six months before the last one expires? I don’t think this will matter - your dog will still be covered against rabies. The important thing is not to have gaps in between when the vaccines are due. This isn’t quite the most cost-effective way to do it, but I don’t think that’s a big deal if you’re happy with it.
Unfortunately the fact is that most veterinary vaccines are given much earlier than it’s probably necessary because it’s not in anyone’s financial interest to do the studies to show that immunity lasts longer!
(Caveat - I am not a vet but I am a professor of human infectious diseases)