I can't speak from experience, but my feeling is that being a "deadname" means they want to push it out of their past, as not part of their real self. I get that, but it doesn't change the fact that at one time they were a different name with a history. It's a little different than a name change from a marriage. I agree on the need to know aspect. What I'm wondering is how do you provide references of past jobs if they were under that name, but treat it as a no-go for the company?