I was a first day reservation holder and a previous owner of a Model S. I've already received my my car in early March and it's been wonderful. So wonderful in fact that I've just reserved a second one for my business this time.
I've done some searching and didn't find any threads in this situation so I thought I'd document it for others to see if/when the priority kicks in. Hopefully it's helpful. The rundown so far:
December 2014 - Received my Model S
March 2016 - Reserved
December 2017 - Returned my Model S (lease)
January 2018 - Ordered my LR Midnight Silver Model 3
March 2018 - Received Model 3 in NV. What a car.
16 March 2018 - Placed a reservation for a section Model 3. Currently says "Late 2018"
I'll update as things progress in case it's helpful for others who decide to go with a second reservation late in the game. (And if others have taken a similar route, feel free to chime in.)