Like the subject said.  I have a stave with not much width that has a horrid check down the middle.  Sitting in the "burn if it gets cold" pile but just saw a butterfly spline done with a completely unrelated project.  My thought is it would cause an issue on the back left bare unless it was backed with something else.  Just curious and if there is another post like this that has it answered pretty please direct me there  

Goose, unless the check runs off the stave you shouldn't have to worry about it. Fill it with super glue(not even necessary) and get to tillering. I think adding a butterfly spline would only complicate the matter.