Depends on the size of the run.
I'm surprised 12D are getting 2. With a 24 pair run usually we get one pair. I think most retailers order 2 pairs of the more popular sizes (8-10) one each of the small and large sizes and perhaps 1 pair each of 8E-10E
Don't forget about the people who require narrow or extra wide as well and those 24 pairs are gone in a hurry!
If it is a small run like the Whiskey WTB (12 pairs) forget it.. every man for himself!