I don't know if the judge will allow this charge to stand as a legally chargable offense or not, but I believe you do not understand fully the legal nature of this. I've read many legal experts who have claimed that the offense was already implicitly in the law before the act was committed and therefore can be legally charged. The legislature added the specific language later just as a way of saying, "if you didn't already understand this, then let us make this perfectly clear, this is against the law."

Again, I'm not saying that the judge might not possibly throw this out, but it's very debatable as to whether or not it was already on the books.