Conferences created to be long running (no end time) can be edited manually to include late registrants.
If a Canvas BigBlueButton Conference activity has already been created and students are registered to the course at a later date they can be manually added to the Conference activity.
Note: This only applies to long running conferences; conferences that are in progress or have concluded can not be edited.
To add late registrants:
Locate the long running conference you wish to update, click the cog wheel icon, and select edit.
Then choose invite all course members  and select update  to save the changes.
Refresh the Conferences page.
All course members, including late registrants, will now have access to the conference and ability to view any subsequent recordings.