Being over 3 decades post everything and, as you would put it, (I really despise this term) "passing" without question I have the luxury that every single time I choose to offer it up it is freely, because there literally hasnt been a single instance in well over 25 years when I have been forced to disclose. Of course I would always say that I have a "trans past", rather than a "trans present", as having long since had GRS I no longer percieve myself to be at odds with my sex.
That said I don't approve of hiding my past as if it is a guilty secret, neither do I approve of wearing a tee-shirt banner advertising it. Therefore the times when I freely choose to disclose are those where it will have maximum impact, and make people realise that their image of what this all means is wrong.
One such occasion came in my first term at medical school when we were being introduced to trans issues, and of course it was all being presented as some sort of slightly strange and unusual condition that my fellow students, who had by then elected me as their year representative, would be unlikely to ever encounter.
I stood up and announced that this was in fact so "unusual" that their own year rep had undergone tretment for it in her youth. That deeply shocked a lot of people - students and staff, because as someone said, "I never would have expected that from you" but it helped them to see it not as some oddity but as a normal medical condition, which can be treated, and which deserves full respect and consideration.
Hopefully they will all be better doctors as a result. That is the sort of situation in which I will freely disclose.