The case was to roll forward a physical standby with an RMAN SCN incremental backup taken from primary. The standby database was just restored and necessary archived logs was missing somehow (That's another story). It was something i already did in the past so we set to work with my previous notes. Took the backup, copied files to standby server and recovered standby database. But the problem was, RECOVER DATABASE NOREDO statement was doing nothing so media recovery was asking for the same archived logs.
Cross-checked the steps with Data Guard Concepts and Administration Guide there was nothing we were missing.
And then after the warning of my team-mate, checked the note on MyOracle Support "Steps to perform for Rolling forward a standby database using RMAN Incremental Backup. (Doc ID 836986.1)" and voila! My note and Administration Guide said "check the SCN on the standby database using V$DATABASE" and support note was saying:
"You need to use the 'lowest SCN' from the the 3 queries below"
SQL> SELECT CURRENT_SCN FROM V$DATABASE;
SQL> select min(fhscn) from x$kcvfh;
SQL> select min(f.fhscn) from x$kcvfh f, v$datafile d where f.hxfil =d.file# and d.enabled != 'READ ONLY';
Again, in my case no media recovery was run on the standby and the control file was not sync with datafile headers.V$DATABASE gives information about the database from the control file and it was not the SCN i need on the incremental backup. I need the minimum SCN information on the datafile headers and that information is on x$kcvfh(Kernel Cache Recovery Component File Headers). Each row returned from this view is populated by reading the header off files on disk. While searching more on this view i realized it gives important information specially on problematic recovery cases.