When you recover a database, the database needs to know "what it is", ie, what are the datafiles that comprise my database, how up to date are they, etc. It gets all of this from the controlfile.

The "kcratr_nab_less_than_odr" indicates a potential controlfile corruption (pro tip: if you get an ora-600, call Support *before* doing anything to make sure you don't get yourself into a worse spot).

Because of that potential corruption, we are telling the database to use a We are using a BACKUP (ie, not current) controlfile. That means we can use it to locate the datafiles but you CANNOT rely on the controlfile to indicate how up to date the datafiles are, or where potential archivelogs could be located for recovery etc, and we cannot rely on its contents to tell us when the recovery is complete DONE.

So now we will start with the datafiles as is, and use the init.ora parameters to locate archive logs and keep recovering until you say stop (cancel). We cant automatically work out when the stop, because are cannot rely on that information from the backup controlfile.