The retention time with oracle flashback logs are exceeded than db_flashback_retention_target?

I've found out the retention time with oracle flashback logs are exceeded than db_flashback_retention_target on several number of oracle databases enabling flashback database whatever data guard primary or physical standby from one of my customers.

Such as, db_flashback_retention_target is setting 2880 (two days) but oracle flashback logs are generated now during in the period of 5 days. By the way the size of flash recovery area is 1500g and flashback logs are about 400g in 5 days and I've never created guarantee restore point.

I wonder the mechanism of oracle flashback logs real retention time except two number of facts - db_flashback_retention_target and db_recovery_file_dest_size.

Thanks beforehand!

Best Regards
Quanwen Zhao

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