IMO, with such a large backlog of so many images to consider, and a desire to filter by multiple criteria (age, client, destination, policy, type) and decide which to cancel versus which to continue re-attempting... then...IMO (and it is just an opinion) then your only option is scripting.
If you have a Windows based Master Server, or a Windows based Media Server with server rights over the Master... then I might be able to help you... as I have a natty little batch/cmd plus VBScript combo which can filter and report and generate the required "cancel" commands for you... but... BUT... BUT BUT... it is quite a rough script and not for the faint hearted... so... if you have the skills and the patience then I might be able to help you with a copy of them.
It comes in two parts. 1) a batch/cmd script to collect various text/list files from NetBackup 2) a VBScript to read the lists, munge the meta-data, and then spit out 2a) multiple reports/tables via different sorted groupings 2b) a commented out batch/cmd script to perform SLP image cancels.
So, these scripts are utterly safe to run (in the first stage) as long as your environment can handle being listed... as the scripts will change nothing at all, except consume perhaps a few MB of disk space for text/list files.