The pilot was made in 2011/12 and probably finished around 2012/13, and then after that Daron was given approval to begin production on the actual show.
The animation, from Mercury Filmworks, is a little higher quality because she was able to write/storyboard it and then have it animated over, like, the course of a year rather than a bunch of episodes at once. It apparently introduces Star's backstory, shows her living with Marco (who may still have been named "Sol Juan," his prototype name, here), and introduced Ludo and his monsters and featured a fight similar to the one in Match Maker, minus Skullnick and her romance.
Star was still voiced by Eden Sher here; everyone else was probably different since it was prior to the actual series. Marco and Star look a bit different and the show was known as "Star and the Forces of Evil."
It has never been shown publically, at least not yet; this is information I got from reading Daron's blogs and stuff.