An administrator can enable the recordings table to include recordings that belonged to deleted activities.
If the activity is deleted, the references to the recordings are still in the BigBluebuttonBN database. As long as the plugin is not uninstalled, the recordings can be accessed.
There is an option in the settings for allowing recordings from deleted meetings. 
When this is enabled, using the type recordings only should let you see the recordings from deleted activities in that particular course.
Now:
When this is enabled, recordings from deleted activities may be even imported by default for new activities.
However, for the existing ones, the teacher may need to enable the option manually by editing the activity (if allowed) in the recording settings menu.