The commercial data tape industry cites 30 years as the nominal lifetime of data on magnetic tape. That's way longer than the viable life of a tape technology, which means how often we transition to new drive types. In any case, it's healthy and recommended practice to move data across tapes at least every few years, to assure that the tape pack layers don't adhere to each other, and to validate that the data continues to be readable.
Richard Sims
