Rs23A On Odd, Not Old, Paper?

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.

The paper was coming from multiple sources at the time. So they just used whatever was there at the time. It's old paper. It's very thin and hard and they were starting to run a bit low on ink so it is not as strongly printed as it might have been.