Spread out.
Keep in mind that a car carrier can only haul 8 or 9 vehicles at a time anyway. An Autorack (aka train car carrier) can hold 20 - 24 vehicles, depending upon their size. AND the other minor detail that a dealer may need delivery of more than 100 cars each and every month, just to maintain the inventory they have on the ground.
So what's better? Sending a dealership 100 new cars all at once, which means the shop and service crew that has to PDI each and every car has to do that, as well as that dealership has to find parking for 100 cars that they may not have room for on their lot, AND that you're also having to do that to maybe 40 dealerships in your area? (Keep in mind again, you're talking 12 semi truck loads, ALL at once.)
There's a reason why logistics is what wins battles in combat. The same thing applies here - you've got to juggle things, so a dealership gets maybe 3 truck load this week, then 3 next week, etc., so they're continually refreshing and more importantly, simply replacing the inventory on what has sold the previous week.