Overall Copyright Statement Guidance
Generally speaking, copyright notices are no longer required in order to create or protect your copyright rights, but can be helpful in certain instances. The general rule for copyright notices is that it should include the © symbol, the year of first publication, and the name of the copyright owner. With websites, there is a genuine question of when the website is "first published."
Because the date included in the copyright notice is the date of first publication, a range of dates is unnecessary. That is the year would be "2010" or "2013" rather than 2010-present.
Here are some specific examples.
OpenStack LLC notice
When a webpage is run by OpenStack only and is substantially revised or updated, the copyright notice should include the year that the content was updated. In a Nova dev doc page, for example, the copyright notice should be "© 2013, OpenStack Foundation" if the content has been updated this year or "© 2012, OpenStack Foundation" if the content was last updated in 2012.
US Government copyright notice
For the government copyright notice, if the material you received from the government has not been substantially revised or updated since you received it, do not change the year on the copyright notice.
Multiple copyright holders
If you update a page, you can add the entity you represent (self or organization) to the list of Copyright holders, but do not remove any listed Copyright headings. If the content has been substantially updated in 2013, add the year to the change. If no substantive updates or revisions have been made to the copyrighted material, the year does not need to be updated.
The RST files in developer documentation and the DocBook files in operator documentation handle copyright statements slightly differently but these general guidelines apply no matter the doc file format. You are not required to add a copyright header to an RST file. Ideally the Apache header will suffice.