given the changes in tape technology, how many tape drives do you still have around that can read tapes written in 1992 reliably?
if you are doing long-term archiving, no single copy is a valid long-term storage. In every case you need to have multiple copies, with error correction, and test them frequently enough so that when one copy fails to read you can still get the data from one of the other copies.
you should be migrating your data from one generation of backup to another on a frequent basis if you are doing long-term archiving.
However, most people are not talking about long-term archiving when they talk about backups, they are talking about disaster recovery, getting the systems running again with the data that is online and available just before the disaster. For that you need multiple copies, and geographic distribution of the copies, but you don't need to read media that's been in storage for 20 years.