I can't remember the exact court case but it was held that it was a breach of something to insist that transexuals had to have had surgery and/or hormones to achieve the protected characteristic of gender reassignment.
So if it is about degrees of transitioning then the TRAs will complain about genital inspections.
On the point they made that the SC deliberately didn't refer to those "who have undergone" transition, if the SC had intended those who have undergone transition could be included as women, don't you think they would have gone on to say that explicitly? The have undergone transition was probably left out because they forgot, could not be arsed to write it out or they thought it was covered.