Apologies if you know this already and I'm preaching to the choir.
But if you get a pet passport (and it's a really good idea to do it) just make sure the date entered for the rabies vaccination isn't any earlier than the date the vet enters as the 'chip implantation/read' date.
Most vets will put in the chip date as the date they read it (as they didn't actually do the implant). That will therefore be the date that they are issuing the passport. So - if they just copy the date of the last rabies vaccination from your AHC, it will be an earlier date; and the passport won't be valid yet.
To make it valid, you need a rabies booster with a date no earlier than the 'chip read' date. Then, the passport is valid 21 days later, after the rabies vaccination has become fully effective (use your AHC to return if you need to).
So the easiest way to be sure, is to get a rabies booster at the same time as they do the passport. There's no harm in that, it's an inert (dead) vaccine and it actually used to be commonplace to give two anyway, to bring the antibodies up to the required level.
And any future rabies boosters need to be done in the EU, a UK vet entry for rabies invalidates the passport.
