Mortal Kombat - April 19, 2011 Mortal Kombat: Komplete Edition - February 28 2012
Mortal Kombat only had 4 DLC characters though. I'm guessing if Injustice only has 4 planned DLC characters, NRS might release a "Injustice: Complete Edition" sometime in February 2014. But if they have more than 4 DLC characters (like if they do a second "Season Pass" thing for another 4 characters) I think it they will wait several more months before doing a "complete edition". Maybe late 2014 or somewhere around there.
So it won't be just a 5 months wait. It will probably be a year, or even more. In fact, if the new generations of consoles are out by then, they might not even bother doing a "complete edition" and just move straight on to working on the next MK game.