In the past, with old analog tape, when analog waves (like VHS video) were stored on metal particle tape, the pull of earth's magnetic field over time tended to magnetically neutralize both 1) the shorter wave lengths of the analogue signal and 2) the weakest magnetic analogue signals. As a result, the image quality of analog video tape would degrade over time -- without even playing the tape. However, the majority of problems with older analogue tape technology resulted from the polymer backing on the tape itself. With frequent use, tape stretch occurred. Also with use, breakdown in adhesives in the backing that held the ferric oxide to the plastic backing itself. The result was color shifts, snow, and synch distortion errors. When issues with adhesives occurred, the ferric oxide literally came off of the backing -- clogging the play heads with ferric oxide. Longevity of old analogue tape was about 7 to10 years.

Now, with modern digital tape technology, digital data -- only digital bits  -- are stored on tape. Magnetic neutralization of a signal by magnetic pull of the earth is minimized by virtue of the simple fact that a "weak bit" gives the same picture quality as a "strong bit".

In resent years, the "sort or strength" of digital tape technology has improved as the magnetic formulas have changed from simple ferric oxide to evaporated metal tape -- making magnetic holding power much stronger.  Also, new and improved are the tinsel strength of digital tape and adhesive bonding properties. Bottom line, the longevity of the better grades of modern digital tape are now estimated in terms of decades -- not years. 

Because of the superior properties of digital tape, both the Data Processing Industry and the Motion Picture Industry relies upon digital tape for "archives". Digital tape it's still very popular for short term backups and off-site and off-line storage. Metal particle tape is an "archive worthy" media for both digital data and for digital images. The only disadvantage of digital video tape is that data retrieval is linear. Data must be read from the digital video tape in real time.