The ‘restore database validate’ only check for the latest database backup. If you also want to check the archivelogs you should run:

restore archivelog all validate;

that will check the archivelogs based on the retention policy of your database. If you want to restrict this validation to the last 3 days of archives , use:

restore archivelog from time ‘sysdate-3’ validate;

Make sure you also check the controlfile and the spfile with:

restore controlfile validate;

restore spfile validate;