If a Googledoc is not shared to all to read/write, then updated material must be "republished" under the share menu. Otherwise, the only people who can see the updates are those who are specifically invited as collaborators. The doc's URL remains the same.
I e-mailed a group presentation doc to a supervisor. All group members were able to continue updating links and other content to the doc without having to e-mail the supervisor updates. The supervisor's access to the doc was read only, while the presentors could read/write as collaborators of the doc.