Google's John Mueller said in a webmaster hangout video that Google can show either the original published date or the last modified date of URL in their search results snippets. He said they are flexible about these dates and if the content substantially changed, they may use the last modified date as opposed to the first published date.
He said this at the 11:16 mark into the video:
Question:
Why do search results sometimes show a publication date and time instead of the last modification date and time? Wouldn't it be useful for the user doing it the other way around?
Answer:
That's something that we we sometimes argue with with the dates team. But I see they're good arguments both ways. And in our algorithms we don't always pick like one or the other as the one that would show.So sometimes we feel that the original date makes sense the show sometimes it makes sense to show the last modification date where we know that something significantly changed on this page that affects what the user is looking for.
So I think there are arguments that could be made for both directions. And that's kind of why we try to be bit flexible there with the algorithms.
Of course, we know Google gets dates wrong often in search and it is something they continue to work on - in fact, as you can see above, Google has a "dates team" simply devoted to figuring out dates of content on the web.
Here is the video embed:
Hat tip to Deep Crawl for spotting this and @glenngabe for tweeting it.
Forum discussion at Twitter.
