One important aspect is that McGraw-Hill ConnectEd no longer clears student rosters from the previous school year. When they did that last year, they accidentally wiped out data from schools after the school year started. So they have stopped that practice.
Delete last year's classes/rosters - Limited Student Licences
So all teachers will now either need to delete last year's classes to free up student licesnes or delete all students from their ConnectEd classed. Otherwise, there may not be enough licenses to go around.
Below are some ConnectEd guides.
When you login to ConnectEd, there is a Help link in the upper right portion of the main screen that provides additional tips and guides.