The terms of the more recent law always take precedent.
My understanding is that change an occur is Judges consistently interpret a law in a way that could be said to be slightly different to the original intention.
So if prior to Haldane any number of Judges had ruled that the phrase "for all purposes" was too vague and the fact that the SSE were written identified that in reality the law recognised that women are biological females, she might have made a different ruling.
But it is clear that unfortunately, more and more we cant rely on political campaigning and lobbying, but have to hope that a legal case will either clarify a law, or even mean it has to be redefined.