Answering a question on whether it would show manual actions dating before the launch of the Manual Action Viewer, Google said it will definitely show a manual action, in case one existed prior to the launch.
The question was posted by Barry Schwartz of Search Engine Roundtable on Google+. The question was:
“+John Mueller The Google Manual Action viewer launched in August 2013, would it have shown manual actions received prior to the launch (if they still existed), let's say dating back to 2012?”
John Mueller, Google’s Webmaster Trends Analyst, confirmed the query with an affirmative answer saying, “Sure, if there's a manual action, it'll be shown.”
The Manual Action Viewer was introduced to the Google Webmaster Tools in August 2013, allowing webmasters to see if their site had any manual action applied to it. So if paid links point to your site, if you are hiding text or you have user generated content spam- Google will show it to you in the Manual Action Viewer, without having to send you an email about the same.Google says it Shows All Manual Actions in Manual Action Viewer, Even Those Prior to the Launch of the Tool!,