Google led me to this doc. i infact was concerned with 1.9. (so i changed the url)
the 'previous versions' block only links to the main page. It would be nice if there was a link to the current page in the 1.9 version.
if it doesn't exist, maybe say so somewhere.
Edited by Helen to add:
The 2.0, 2.1 and 2.2 documentation wikis contain many pages with the same name in each wiki. It would be very helpful to provide links to these pages
e.g. http://docs.moodle.org/22/en/Authentication would have links to http://docs.moodle.org/21/en/Authentication http://docs.moodle.org/20/en/Authentication and if possible also http://docs.moodle.org/19/en/Authentication
Also, when editing a page, it would be helpful to have a message at the top of the page stating which version the user is in and providing links to pages in other wikis.