On further analysis, it would work best to be able to select which of the additional roles of Editor, Author, and Contributor could use one or more selected Invite Users pages.
If the above is too difficult, it would be workable if the Editor and Author roles could use the Invite Users to Register page.
My timeline for being able to use this added role feature is two weeks from today: September 16, 2018.
Go to the WordPress Settings > General. Uncheck the box for Membership, Anyone Can Register. This will block registering the usual way, and will allow registrations only through Invite Only emails that you send out.
