I received this response from smartusa in reference to my inquiry as to why invitations to confirm seem to be out of sequence using reservation numbers:
"Dear smart Enthusiast, The last digits in your confirmation number are not related to your place in line, but, rather a randomly generated number which is tied to your reservation. Our system shows that you have not yet been invited to configure your vehicle. Over the next few weeks and months, groups of reservation holders (in order of when reservations were placed in their area) will be contacted by email or by phone to participate in the next step of the reservation process...."
This would explain how res number is the 1500s are getting confirmed before 1200/1300 numbers.
It was my understanding from the beginning that the last four digits of the number were a code indicating the number of days into the reservation program that a reservation was placed.