I face this issue when my tivoli admin friends warn me about old backup which could be listed on Tivoli Storage even I delete my all old RMAN backups wiht RMAN commands on our 11.2.0.1 databaseI have 11.2.0.1 database on AIX 6.1 which we use RMAN backup utulity  wiht  RMAN catalog by using tivoli.

First i connect to RMAN catalog,

RMAN> show all;
RMAN configuration parameters for database with db_unique_name PMUH00 are:
CONFIGURE RETENTION POLICY TO RECOVERY WINDOW OF 8 DAYS;

than run below rman commands to delete my backup which is older than 8 days;

RMAN configuration parameters for database with db_unique_name PMUH00 are:
CONFIGURE RETENTION POLICY TO RECOVERY WINDOW OF 8 DAYS;

run
{
ALLOCATE CHANNEL C1 device type ‘sbt_tape’ ;
delete force noprompt obsolete;
RELEASE CHANNEL C1;
}

After this command i checked belows

RMAN>  LIST EXPIRED BACKUPSET;
specification does not match any backup in the repository

RMAN> LIST EXPIRED BACKUP;
specification does not match any backup in the repository

also report obsolete doesnt bring any data, but my tivoli admin friends keep saying me they see still old backup.

We noticed that When an RMAN delete command is run, RMAN deletes entries in the recovery catalog before confirmation from the Tivoli Storage Manager server.

We followed below docs and we solved problem:

Remove Backups From Tivoli not available in RMAN catalog [ID 1209740.1]