I picked up a RS23 and at first glance it looked like a nicely centered copy without the usual faults. I then noticed the color was a bit off, more grey than black & white. When I pulled if out the paper is very thin, more like paper that a proof would be on. I've seen plenty of RS23s and this is not old paper. I suppose someone could have perfed a proof, but that begs the question as to why.? The RS23 proof is more valuable than a RS23a.