Google’s John Mueller said it is great to go through old content and make sure it is still valid and accurate. But doing so doesn’t mean that you should update the date of the content to the date you reviewed it. If you want to inform the users who are reading the content that the content is still valid, maybe add a note to the content John said. He said this on Twitter when someone asked about how he can handle such content. Here is the Twitter conversation: Again, I said it before, I would love a no date penalty and a false date penalty (which Google might have). But there is something to be said about someone going through old content and validating that content is still true. Forum discussion at Twitter.