Two things. First, your timeline seems too short. There's the 6 month wait from the date of a good rabies titer (the blood test). The 998 form, once filled out by a USDA-approved vet and signed and stamped by the USDA (the official USDA vet for your state) is only good for 4 months from the date signed.
Unless I'm misunderstanding you, it seems like you should wait at least 2-3 months from the date of the rabies titer before having the paperwork done and stamped, because otherwise, it'll expire before your pet can be transported.
As for the different vets, there's the USDA-approved vet who does the blood tests and fills out the paperwork and then there's the official USDA vet for your state who stamps/certifies the paperwork that was filled out by the USDA-approved vet.
It's confusing, but they're not all the same person.