Disappearing clip

Here's one I have never experienced in fifteen years. I have a FCP 7 timeline and I backed up all the clips to a second harddrive. The startup harddrive crashed and when i replaced it with myh backup, all worked fine except one important clip was mising from the timeline. No problem, I thought. I went into the folder and it was missing, just not there. I went to the backup drive and it was gone too. I did a Search and it was gone. This I cannot understand. How can a clip disappear from two harddrives just because the startup drive crashed? Any ideas? Thanks to all of you for great help over the years.