The Mystery of a Mystery

I've been cleaning out computer files, paper files, nail files, and forgotten files this past week. Sometimes, I come across something I wrote a long time ago. It usually triggers a happy memory, shortly before I bury it again in another file label, "Not Until After I'm Dead." But one file I came across is an outline for a mystery, complete with some character sketches, and an almost complete outline. It's an electronic file, and I can't imagine someone sending me something so clean, if a bit incomplete, for a critique. But, I have absolutely no memory of having written this in 2005. I'm afraid to pick it up again and work on it, fearing it might actually be someone else's and all the work I do with it might be for nothing.

Has this ever happened to you? If so, what did you do about it?