I don't know if anyone else experiences this or not but it's kind of an hassle. Google is using dates from the related topics table to grab the oldest and apply that as the indexed date related to the entire page.
I have a particular situation in a thread created two weeks ago that Google returns as being from Apr 2012. Apr 2012 is the oldest of the related topics that this topic has.
Does anyone have any pointers on this? I found this:https://support.google.com/customsearch/answer/2364585?hl=en
And I'm trying to get it setup, but I don't know if it will help or not.
Edit: I'm thinking that most likely the best way to prevent this is to make the related topics available to logged in users only.
Edit2: I opted to just hard code it:
$context['user']['is_logged'] ? $topic['last_post']['time'] : ''