It depends on the weather as far as how late. I have found them as early as late August and as late as around now (Late Oct). I think I remember finding them in early Nov one year but they would not be new ones ut older ones that have been up for a while.
Old hens from last year are usually as dark as chocolate and decomposed badly. If they are old white or cream color ones they are most likely old chickens.
I would think down your way they would go into November and not sure about if it's too late for a helpful rain down your way.