For Aux Copy as the Jobs are being copied to Tape they will be marked as "Partially Copied" only when all the data is written to Tape then the associated Jobs will be marked as "Available"
If the Aux Copy did complete with errors you can try to re-run the Aux Copy to see if the initial errors are transient.
By selecting jobs for "re-copy" you are choosing to invalidating the data written to Tape, and start a fresh.
During the Aux Copy Process the data blocks on disk is read and verified before it is written to Tape. So in saying that during the Aux Copy process you are pretty much doing a verification before it is committed to Tape.
Additionally once Data is Aux Copied to Tape you can also opt to do a Job-based Data Verification on Tape (which will take time), which will also re-verify the writtent content on Tape.
If you are seeing more errors or Aux Copy "completed with errors", I would recommend to engage Commvault Support to verify further.
Note - you also have Incremental DDB Verification which is ran automatically (assuming it is enabled) to also verify the Backup Jobs written to Disk.
Overall there are various verification process that runs in Commvault to ensure Backup is correctly written to Disk and Tape.