I recall being on a weekend drill, camping and during the day we had A-10's flying low overhead, fast. I could see them looking up past the pine tree cover above us. Someone then told me it was just one A-10!
They've trained above our farm for decades. I would be surprised if there were "just one". They typically have a two-plane echelon, with the trailing "wing" separated by a fair distance. I suspect this formation allows the wing to respond when the leader draws ground fire.