The proposal was not retrospective, it was prospective. For it to be retrospective it needed to apply to years before the introduction of the legislation, For example if the law was amended in May 2019 to apply the the 2019-20 and later financial years, that is not retrospective. It would only be retrospective if it applied to the years before the law was legislated, e.g to the 2017-18 or 2018-19 financial years. Unfortunately too many people don't understand the meaning of retrospective.
