If you have no idea of the tape you need, you are in a world of hurt. Using import to import a bunch of tapes is very time consuming.
Your best bet would be to try restoring your client catalog info and manually checking the images.
If you are on unix, I would suggest you set up a process that sends you information that you can refer to:
/usr/openv/netbackup/bin/admincmd/bpimagelist -media -U -hoursago 48 -client CLIENT
I am setting up a series of these to store a list of tapes in a file for referral in a DR situation, so OPS can open a file for an application and see what tapes will be needed to restore it.
If you had this in place, you might be able to determine old tape information.