I hadn’t shot many late season doves until a few years ago and after making several hits on birds that kept going after leaving a pile of feathers floating down. I started shooting #6 shot on late season birds with the thicker down. I know #8 is still fine on a good shot but the marginal hits and higher birds the 6 brings them down better. Less wounded birds. And I really haven’t seen much more destruction of the meat.
The migratory birds we get in the late season are bigger than so many of the young local birds we're hunting in September; I shoot 7 1/2 shot on the bigger birds compared to #8 early. May not make a huge difference, but that's been my preferred choice over a lot of years.
The birds you shoot in September are in large part first year birds that we hatched here, which is why you kill a lot on which the feathers aren’t fully developed. By December nearly all of the birds hatched here have move south and you are shooting migratory birds that were hatched North of here and moved down. They are generally bigger overall because the young birds have had 3 months to grow and plum out, and typically a little more skittish because they have often times been shot at all the way down North America.
Cooler and the birds come in bigger groups. Migratory birds are really spooky they can be there today and on your neighbors land tomorrow. So when you see them you better shoot them. Don't use cheap shells.
Also, most row crop fields have little food remaining by the time January comes along, so whoever has a field with food in it has a huge advantage. Take that as you will. If your field has food, you can have a barnburner.