If you need to recover from those older backups to disk, you need to create a copy to tape, then once all the data has been copied (that you need to keep) promote that copy to primary, and then delete the old primary copy. Do this for all the policies that wrote to that array (as primary).
If those backups have already been "aux-copied" then just promote the tape copy to primary and delete the original disk copy. This will erase all the data written to the disk array. Just be sure that the retention for the tape copy is set to meet your retention requirements. You can still keep/use that policy for backups as once the tape copy has been promoted to primary, all new backups will go direct to tape.
Let us know if this helps.
Ernst F. Graeler
Senior Engineer III