I feel like this is a needle in a haystack situation, given the number of trans threads, but here goes.
Recently there was a good post on a thread from an older trans woman (think she used the term transsexual), setting out the establishment of the original legislation around GRCs, including number of people affected, the decision to use "gender" not "sex" in that legislation etc.
Can anyone remember this and recall her username? So I can find the post again. Many thanks.