This question was answered on Wednesday.
See  http://www.mail-archive.com/adsm-l AT vm.marist DOT edu/msg79579.html

On Dec 26, 2008, at 8:39 AM, Cheung, Richard wrote:

Hi all

Just a quick query to round out the year...

Lets say I have two media pools, a on-site tape pool called LTO,
and the
offsite copy of this LTO pool called COPYPOOL.

If I have generated a backup set into my standard LTO media pool, will
these tapes which are holding the backup set then automatically
also be
copied into the COPYPOOL ?   If that is the case, are there really any
need to me to explicitly check out these 'backup set' tapes out of my
LTO media pool / library - when there may be already an offsite copy
automatically generated into the COPYPOOL ?

Please advise.

Happy Christmas and a safe and joyous New Year to everyone