I've known of a couple pre-finds in our area. In one case, after a cacher used a phone-a-friend for help, the friend told them of his "yet to be approved cache" in the same area as the other cachers were in. He supplied the coords, and the other cachers found it before it was published. They signed the log book on page 10 or 12 (or some page other than the first couple) and didn't date it. Then after the cache had been found and logged a few times on GC.com, they logged their find.
The cacher who claimed the FTF never knew that the cache had been found the night before.