Not sure where you've got the 'few dozen' number from - that's not to my experience. Tandberg quote "1,000,000 passes on any area of tape, equates to over 20,000 end to end passes/260 full tape backup" http://www.tandbergdata.com/default/assets/File/Data_Sheets/...
Atleast from what I've been told and from experience, if you rotate over master backup tapes every few months, the tape will be almost 6 years old by the time it reaches the first two dozen end to end writes, that usually means newer LTO standards, newer drives and newer tapes on the market to replace them with.
> 1,000,000 passes on any area of tape, equates to over 20,000 end to end passes
What in the world does that first number mean?
My best guess is that it's some nonsense math based on the fact that the tape head contacts 32 tracks at once. So writing a full tape is 1 "full pass", which equals 208 "end to end passes" as the tape feeds back and forth, which equals 6656 """passes on any area""".