In Canvas Conferences, when a conference is created it is accessible only to those listed in the Members section.
When you create a Canvas Conference, Canvas automatically creates an associated "access control list" (ACL) of course members that access the conference and view its subsequent recordings. You see this as Members of the conference.
By default, the Members list for a conference comprises all students enrolled in the course at the time you create the conference.
Also, when creating the conference, you can edit the Members list by unchecking "Invite All Course Members" and choose the specific students you want to have access to the conference.
For example, in the above screenshot, John Doe and Jesus Federico in the Members list for the conference. Only those two users will be able to see the conference, join it, and view the subsequent recordings.
When a student is added to the course after a conference is created, they are not automatically added to the Members list.
In this case, the student will not be able to see any previous conferences, nor view their recordings, because they were not a member when the conference was created.
As long as the conference is in progress (not ended), you edit the conference and add more students to the Membership list.
Alternatively, you can use the shortcut "Sync Attendees" to have Canvas add all current course members to the access control list. This make it easy to quickly add members enrolled in the course after the conference was created.
If the conference is concluded, there is no ability to edit the membership list anymore.
If you are on the Premium Tier hosting (you have a hosting subscription with Blindside Networks), one solution is to provide direct links to the recordings to late comers. That is, as the instructor, when viewing the playback of a recording, copy the recording URL and share it with the students.