If someone has been invited to access the working group list, a small orange icon will appear next to that person's name on the list. If you mouse over the icon you should see the word "invited."
To invite anyone else, simply check the box next to their name(s) and click the "Circulate List" button on the right, following the prompts from there. Once you hit send, the invited icon should appear next to the names of those people also.
You can resend invitations to people if you want or need, but they will be apprised of changes to the list via email digests. For more on those, see FAQ entry "How do digests work?"
Keywords / tags: invite, inviting, invitations, circulate, publish, add, new, digest