Mark, I tried reading an old Notebookdrive from 1997 recently, not much luck. It sounded good, no alarming noise, but I couldn't get at most of the files on it.
The drive was removed from the notbook early 1998 and replace against a bigger one, the file in question was my former girlfriends thesis. She lost the CD with the MS Office files, which would be useless anyways without Office 95 to read them.
I then got the old QUIC tapes and a Tandberg tapedrive out of the cellar, found the tape with the PDF, which was mostly unreadable, found the tape with the MS Office files, which was mostly unreadable, and found the notebook harddisk, which was mostly unreadable as you know by now 🙂
In an old filing cabinet in my office I found some old Kodak WriteableCD from late 97 which were readable without a problem. It was the complete backup of her Notebook including Win95, Office95 and her thesis 🙂
Make it 9 years proven reliability for CDs and less for HDs and tapes.