Ani-May has been on an overall decline for me since 2007, not surprised to see that's when the overall amount if original works drastically fell.So CR based a whole news post on a spreadsheet of anime from 2000 based on the source material from a reddit user.
http://www.crunchyroll.com/anime-ne...terial-for-anime-over-the-last-decade-charted
Interesting stuff. Though I wish it went further back, though I guess details of source material for older stuff is no as available.