* I don't think labels matter. *
Ah so? Now really? Male and Female labels matter one heck of a lot for the latest US security issues just for a starter, also they do matter LOTS in hospitals, see my comments below.
It's too easy to just state "labels don't matter" in fact if you ask me they matter one hell of a lot, lest you own a car and it's a bicycle and it makes no difference either, just by example.
Our WHOLE world is made up of labels!
A valid question the OP asked, if you go for instance on any dating site, or hospital, etc. stating your SEX as being Female.
I'd think for pre- and non-op to say YES, be not quite the truth, or?
Post-op... I guess it be 'correct' - YET NOW IF MY ID SAYS OTHERWISE??? Checking between my legs then? Maybe...
It will take over ONE year for either German and SA authorities to just get that done (to change my ID)... say no more!
Yet, most correct for post-op MtF be SEX = female ------------ with a transsexual history...
in case they want pap-smears, and try to find your uterus, ovaries, there be none, and no hysterectomy scar either... yes?
Now let's see what else be suggested to the OP's question.
BTW, the same be true not only for MtF. To answer SEX = Male, with all those girl part present......... well? Go get a prostate check-up, and get tested for testicular cancer? Really? Hum.
Axélle
PS: Just my personal opinion mind you...