Normally tapes are written over every six months- year, but first they are sent offsite for copy to virtual library. The idea that they simply write over takes every 6 months without first archiving is hard to believe, especially given id the IRS, not joes landscaping. After vendor archives data onto their redundant system. They are sent back to company and go back into production and are recycled every six months or so. This allows admins do restore user data on site if within six months. If beyond six months they procure from offsite location if approved (depending on critical nature of data). If they subpoena the vendor there is no way to completely delete the evidence, including logs, tracking, forsenics of drive and storage systems traffic, purchase orders, employee names, etc.
Someone I know works at Boeing and he had to agree to not even send emails regarding the Malaysian plane due to possibility of future legal problems.
Where I work if we lose an excel file we just order a restored copy from the backup, and I’ve seen specific time period histories of emails delivered to 3rd parties.