1) SET AUTORECOVERY ON

This command just tell the database that you will recover your database until
final available log file. As I know, this command has to be run first before issue:
RECOVER AUTOMATIC DATAFILE....

2) RECOVER DATAFILE.....

This command let you recover your datafile...
if incomplete recovery, you will be asked to recover until (you have to choose:
Auto
Cancel
or other options)

3) RECOVER AUTOMATIC DATAFILE....

This command is just tell the database that you will recover until final available log file.
Same as second command which you choose Auto.