RMAN question regarding configuring OPTIMIZATION ON and "report need backup" command.

hi,

I have serveral read-only tablespaces for holding old date range partions. Once a month I switch these tablespace to read write and move a new partition into the tablespace and then switch the tablespace back to read only. I wanted to avoid backing up these datafiles every night so I turned optimization on. My rman backups seem to be working as expected - I see the datafiles for these tablespaces are being skipped except after data is added or when the last backup has aged out of the system. Recently I ran the command report need backup:

RMAN> report need backup;