The GCI wouldn't see a missile on a radar screen of his scale. They have a filter applied to them you know, so it doesn't pick up birds and the like.
Consider the size of a missile compared to an aircraft, and consider its speed. It isn't something a GCI could reliably, if at all, track using a radar scope.
I have an idea yeah, I didn't even mention the A-10C TGP so I don't even know where you're getting that.