Lake of Shining Rock print

I found this print in the storage barn at my mother's home the other day. It was stored in a large piece of cardboard in a corner against the wall with other pictures. - It was eventually going to be thrown out in the garbage. I took it in anticipation that it might be worth something. It is a print marked "Lake of the Shining Rock" AP #27. It is complete with the paperwork - Stephen Lyman 27/50 is the signature - I believe it is an original signature on this print. Next to the signature is another signature - Stephen Lyman (c)92 - that signature appears to be in the print. I know that AP means Artist's Proof - does that make it more valuable? It is a nice print in remarkable condition - especially due to the fact that it was probably sitting in the storage barn for 10+ years. Any feedback would be greatly appreciated. The print is much clearer than the pictures show. It is in perfect condition - no fading or condition issues.