It all depends on what they mean as "transitioned".
Currently that means "has gone through male puberty", so in order to be considered "transitioned" then the medical intervention has to be pre-puberty.
What happens if or when Self ID is law and we have fully intact, hormonally undisturbed males being accepted as legally the opposite sex? Will the current Supreme Court judgement affect this?
I can't help but think that messing around with weasley language is a massive mistake. We need the law to be totally clear that sex is what matters and what never changes. You could dig this behemoth up in 1500 years and still tell he was a male, ffs.