I make my Tiffany reservations as soon as I purchase my airline tickets - sometimes even 9 months in advance. Debbie will give you a confirmation number. Then a few days before your trip, I always send Debbie an e-mail to verify my flight information because the flight numbers and times are usually different by then. I request a driver when I make the original reservation and repeat my request when I e-mail Debbie a few days before the actual trip.
As far as a towncar, I always ask for Ronnie or Ian. If we are splurging for the stretch limo, we ask for Marcello.
If we are reserving a van, we ask that Debbie send one of her own drivers, not to send an outside person.
Debbie is wonderful and will honor your requests if at all possible. Usually the only way you would not get who you request is if someone beat you to them or they are not on duty at the time you request.