If this indicator is what we're thinking it is, I definitely ended up with higher Reservation IDs than what I would've expected given when I reserved. I reserved at ~10:15am in the Palo Alto store (on El Camino) on 31-Mar. Reservation IDs are the following:
5008xx
5008xx+3
Granted, if I remember correctly, the charge to my credit card didn't appear until 01-Apr, but hopefully that won't delay me...