I can't claim to know the specifics of the methods used to determine which dealers received them, but I'm pretty sure it totally stopped at least several years ago. I used to always have my dealer get me the Christmas boxcar. From memory, maybe it was around 2010?
I believe the original program was supposed to be limited to something like only 2 of each DAP item to any dealer receiving them, but that most likely evolved over the years. I know I paid more for the first couple cars either in the secondary market or from dealers other than my LHS. Based on the "only getting 2" premise, I knew I was not one of the top 2 MTH customers for my LHS (figuring people who spent a lot more money at the LHS would (rightfully so) have earned the privilege of purchasing the car since he theoretically had so few available).
Later in the program, I simply told my LHS I was interested in the Christmas car each year and it was included with my regular pre-orders at pretty standard pricing (same discount as Premier at the time, I believe).
-Dave