I'm going through the hatch, match, dispatch list of key life events and I can only think of the birth register where it will be sex rather than gender, and even there there's possible dishonesty in the parents section.
Agreed.
And a GRC can mask that information, if I understood the administrative alterations that it implements.
So it isn't an intact representation, given circa 5000 GRCs. But limited disinformation, at least.
However all other databases of male/female data are amendable upon subject request, with varying levels of supporting 'evidence' required, none of which require a GRC and thus are recording data at odds with both biological and legal sex.
Driving licence, medical records and passports all record gender, not sex.
Hence: they are capturing 'gender'.