The master database records information about all databases of the instance. Hence, the master database in a backup contains information about databases which existed in the instance at the time of the backup.
After recovering the master database, you may need to do the following:
Databases that have appeared in the instance after the backup was done are not visible by the instance. To bring these databases back to production, attach them to the instance manually. For instructions on how to do this by using SQL Server Management Studio, see the "Attaching SQL Server databases" section.
Databases that have been deleted after the backup was done are displayed as offline in the instance. Delete these databases by using SQL Server Management Studio.