Old Undo Tablespace - Expired and Unexpired

Oracle DB: 11.2.0.3

RAC - 4 nodes

I creted a new undo tablespace and replace it on the node 4 on Wed Aug 27 13:49, so it has been approximately 44 hours ago.

I would like to drop this tablespace but I still see expired and unexpired undo in the old tablespace. Since I have undo_retention parameter set to 28800 or 8 hours, I thought the expired and unexpired undo would be gone after 8 hours. How would I make sure that there will be no issue if I drop this TS.

TABLESPACE_NAME,  STATUS,               BYTES

UNDOTBS_04,             EXPIRED,                23,199,744

UNDOTBS_04,            UNEXPIRED,   385,168,048,128