Should there be a tag for the Red-White Sheep series of merchandise as well? It was released on January 31st 2015 in Osaka and the day after in Tokyo, according to this.
Searching for sheep_horns precure seems to get a few examples, mostly Kanade, but I don't know if there are others tagged differently.
Checking the Precure Pretty Store Twitter, apparently it was announced on Jan 21. I don't know if posts before that with the red/white Precures in sheep costumes would count, due to Year Of The Sheep and all that.