Limits on role types to assign?

I noticed that sometimes I can assign a user all three roles, ie author, admin or reader, and other times only author or admin. Is there a limit to how many user types I can assign? This is with the enterprise addition. Thanks in advance!


QuickSight readers can be upgraded to Authors or Admins anytime.
QuickSight Authors can be upgraded to Admins at any time.
QuickSight Admins can be downgraded to Authors at any time.

QuickSight Admins and Authors cannot be downgraded to readers.