How do you know when you've reached a point where stealth is an option?
It's a Catch 22 but you've reached a point where stealth is an option when you are gendered correctly 100% of the time by people who do not know you are transgendered. Getting there is tricky; being outed one time and it's all over. Like the new girl you work with, we can never be sure if someone is being respectful or truly sees us as our target gender. It's even more complicated when it is possible they may know a person is transgender.
Living in stealth was never a choice for me; it was my only option. My female alter and I live separate "normal" cisgender lives. She created a new life for herself when she became self aware six years ago. None of the 5 alters in my System identifies as transgender. It is vital that she and I are perceived by the people in our respective worlds as the woman/man each of us is. Any crossover in our worlds would destroy the doublethink we use to maintain the delusion of being separate people. A handful of people in my female alter's life know she has Dissociative Identity Disorder/Multiple Personality Disorder (DID/MPD). They understand her to be the System host, do not know she has a male body or that opposite gender alters take turns fronting for the System. My wife, stepson, Mother and the medical professionals who treat me know the complete truth. But it would be catastrophic to the Self for the boundaries that contain the feelings and memories held by each personality to break down.
Is my female alter stealth or are the people she knows being polite? I think you have to look at it statistically over the course of day to day life for the answer. In the last 6 years I have put my female alter in every situation I could think of to fail; asking other women in the dressing room how she looks while trying on clothes, conversations with naked women who just got out of the shower in the locker room, chitchatting with women standing in the bathroom line at the beach in her bikini, close friendships with men and other women, accidentally walking into a bar full of drunk navy guys in a wet tee shirt and ruined makeup to get out of the rain, monthly trips for pedis and body massages, having her pants fitted by a seamstress, spreadeagle with one of her girlfriends' hands by her crotch assisting her with a pose in yoga. My female alter has come through every one of these without question or raising an eyebrow. In six years of fronting for my System, 5000+ hours out and about living her life, her femininity has only been ever questioned twice; both preHRT in the first 6 months she began fronting for the System. It is not statistically possible to have encountered so many people in so many different situations over such a long period of time who treated her as a woman to be polite.