I believe that this contraction should be made a legal word, and all contractions of similar nature. There is no reason why, "Would've" should be a word, but "should've" is not a word.
Additionally, I consider "Woudln'tve" a word which stands for "Would not have". I also believe that "Shouldn'tve" should be considered a legal word which means, "Should not have".
If we get this done, we save ink when it comes to printing documents. A similar study was done on "Font Types", but I a digress.
(Link to CNN video below).
Get it done.