HAHA... been there, done that.
The best way I've found is log your jobs into an Excel spreadsheet. My excel spreadsheet has the Job Title, Tape(s) used, Size of backup, how long it ran, and if it completed successful or not. I've been keeping this type of log updated on a daily basis for years now. It has always helped because you can resort back to your spreadsheet, print it out, etc... and collect all tapes from your most recent Full backup, to all Diff/Incr backups that followed it to present day.
I always hated finding that the job would hang up, waiting for a particular tape to be inserted.
Good Luck. Hope this helps.