Mix and Match LT05 and LT04 tapes

COMPATIBILITY: LTO-5 drives are designed with backwards-compatible read-and-write capability with LTO-4 cartridges, and backward read capabilities with LTO-3 cartridges, helping to protect investments and ease implementation.

Source :-http://www.trustlto.com/index.html

What are the backward compatibility characteristics of the Ultrium format?
The LTO Ultrium compatibility is defined with two concepts demonstrating investment protection: 1) An Ultrium drive can read data from a cartridge in its own generation and two prior generations. 2) An Ultrium drive can write data to a cartridge in its own generation and to a cartridge from the immediate prior generation in the prior generation format.

For example: 
- An Ultrium format Generation 5 drive will read and write data on an Ultrium format Generation 4 cartridge as specified by the Generation 4 format and read data on an Ultrium format Generation 3 drive.

- An Ultrium format Generation 4 drive will read and write data on an Ultrium format Generation 3 cartridge as specified by the Generation 3 format and read data on an Ultrium format Generation 2 drive

Source:-http://www.ultrium.com/About/faq.html

hope this helps.