The need for the term "deep stealth" implies that "stealth" comes in degrees. If "stealth" meant 100% invisibility to the world of one's pre-transition life and nothing less, then there would be no need for "deep stealth."
Using Janet's example, I always figured that Andrea James and Calpernia Addams used "Deep Stealth" ironically, since their lives, and especially their business of that name, are the very opposite of stealth, that is, "out and proud." ("Proud," not in the sence of, "Yay, being trans rocks," but in the sense of, "Yes, I'm trans, so what?")
I don't really think that "passing" and "stealth" ought to be used as synonyms or even different degrees on the same spectrum. Stealth, to me, is about one's attitude toward life, while passing is about how one is perceived in social settings. James and Addams pass quite well, but don't try to hide their past. If you want stealth, look at Lynn Conway's life before she was outed. She probably didn't pass quite as well as James and Addams -- if anyone was looking, and perhaps only because FFS wasn't available to her until later -- but even if someone had suspicions, they couldn't confirm them. That's stealth.
I consider them both to be words with highly charged political connotations, so I avoid using them.