Some of antler shedding is based on each buck's tendencies. Year to year, some just naturally drop earlier than others, some later. You can see it in the specific bucks I'm referring to year after year. For example, one I'm referring to wouldn't shed until late march, early april no matter what the winter was like.
That said, for most 3.5 yr old + bucks, their physical condition plays a big role. On harsh winters with limited food, they drop earlier than on mild winters with a surplus of food, as that has a big impact on their physical conditions.
Long way of saying, your deer are in great shape.