I have to ask, how did you get confirmation that you were right? If you asked and hypothetically they responded no, would you simply dismiss the idea?
I think that there is always going to be room for anyone to question the natal sex of another. It's human nature to use mental models to quickly and efficiently categorize everything we see in the world based on a generic template that is constantly being edited, checked, questioned, and adjusted without our ever knowing it.
I have friends of both genders who get misguided occasionally. Even for cis people, the same categorizing occurs, and you can't expect everyone, including yourself to be correct 100% of the time.
I also think pretty much everyone has experienced this from at least one side; misgendering someone or being misgendered by someone. My guess is that when that happens 99.9% of the time neither side is questioning "are they trans?" Or "do they think I'm trans?" They just assume a mistake has been made and move on.
As to how to deal with it. If you do pass quite well, you can always decline to answer or simply answer no. (Lying is also human nature, the social lubricant that gets us through the day).
In this day and age there is raised transgender awareness , which of course makes it more likely you'll be questioned at some point... but so will tons of cis people. It's up to you if you want to confirm this.
We also live in an age where everyone has a digital paper trail. Can't do anything about that. There are situations that you'll have no choice in whether to divulge. My guess is that any background check for any job will show previous names/aliases. Your medical providers will most likely need to know to some degree, especially if something goes wrong, your admitted to the hospital etc.
So while no one, even cis people are guaranteed to pass 200% of the time, you can live in stealth and simply be comfortable with the occasional someone suspecting, but never really knowing.
@Cimara. I think it is possible to pass 100% of the time for the very few.
See this Ted talk.
For me personally, in my adult life before transitioning I had constant male fail. I had to make huge efforts to be gendered as male, and quite often even when fully presenting as male with slacks, button up shirt, tie, facial hair etc. I would still get gendered as female.
Since transitioning I have even had multiple doctors with my full list of medications not have it compute I was trans. Even after just going over my meds, including AAs, estridiol and progesterone I have been asked if the reason for the hormones is birth control, when my last menstrual cycle was, and even after clarifying that I'm trans, being asked if I was m2f or f2m.
So yeah. It is possible, rare, but possible.
In the end I'm just happy to finally be living as me, and the occasional misgendering that I get (the last being at a doctors office, a fellow patient called me pretty, and then switched to handsome as she thought I looked at her weird, which I did- due to a lazy eye, then quickly apologized.) I think that getting the occasional misgendered is simply part of living in a society as a human.
~Brooke~