This indicates a daily build released on May 13, 2013. In software archeology, daily builds often contain unique characteristics that were patched out later.
(Retrospective Analysis) Software Version Spotlight: YTD Video Downloader PRO v4.1.0 build 20130513 Release Date Context: May 13, 2013 YTD Video Downloader PRO v4.1.0 build 20130513 ...
