I have been using bpimagelist to determine the number of byte being backed
up.  My question is how is the data retention control?  When I run
bpimagelist, I get 30 days of data.  Yet, I've noticed that on some
bpimagelist listing, I get data that is greater than 30 days.  Am I right in
that if a tape has expired, bpimagelist will no longer has the information?
If this is true, how does one go about getting a monthly report of total
number of bytes backed up per client per month?

Thanks, 
Ken