There appears to be quite poor coverage of the logic around where blocks can be added.
For example the course_overview block can be added to the default /my page (search site settings for "default dashboard") and manually added or removed from /my by regular users. It should not be available to be added anywhere else.
Manually testing this is fiddly and, I suspect, somewhat error prone. It is the kind of thing that can easily be broken and not noticed until much later.
Every block has a applicable_formats() method that specifies where it can be added.