SELECT SEQUENCE#, BLOCK# from v\$managed_standby
        WHERE process='RFS' AND client_process='LGWR'

with this new one:

 SELECT SEQUENCE#, BLOCK# from v\$managed_standby
        WHERE process='MRP0'

To check this you have to meet the following condition: You should have real-time apply enabled (and possibly NODELAY clause specified in your recover statement). Check it with this query:

SELECT RECOVERY_MODE FROM V$ARCHIVE_DEST_STATUS;

It should be “MANAGED REAL TIME APPLY”.
If not using realtime apply your MRP0 process will wait until you have a new archive, so even if you have redo transport mode set to LGWR you’ll wait for standby log completion. Your gap of applied redo stream will be at least one sequence#.

With transport mode set to LGWR and real-time apply the output of the perl script is similar to this one:

# ./checkDataGuard.sh
PROD   :       1230      20631
STANDBY:       1230      20613
18         blocks gap

The whole gap between your primary and standby database should be LOW.