To tap on to the philosophy side, because I literally wrote my dissertation on how we refer to people and events…
(Please ignore if this bores you, but this is the kind of linguistics that is actually relevant and fun.)
In linguistics, we make a very sharp designation between the “signifier” and the “signified” – between language and what it describes in the world. So that’s a strong distinction insofar as we are absolutely not the same thing as the language that’s used to talk about us. That might seem dumb and obvious but it’s the absolute foundation of talking about linguistic meaning. There is nothing about the word “cat” that somehow is really cat-like. It’s a random assortment of sounds that English speakers have collectively decided will refer to this concept of a small fuzzy four-legged beast with claws and opinions. There’s no mystic connection between the two. That’s true of names, too. There’s no mystic connection between us and our names. In that sense, names don’t matter a single whit; they’re just random collections of sounds.
Obvy names do actually matter, because we care about them a lot. Words are powerful, not because of the words themselves, but because of what they reflect about the state of the world, including human relationships. For names in particular, we often know a lot of background information about a person when we hear their name. We can know local/global origin, parents’ native language, social class, age, gender – hell, we know that they’re human, because most people don’t name e.g. their cars or pets Heather. As both people who bear names and people who use names, we want the information conveyed to be accurate. That matters to us socially. It really hurts us when it feels like someone lies about us or misleads us, or conveys information that’s inaccurate. It feels especially bad when people use the word that conveys inaccurate info after we’ve said “hey, um, here’s some more accurate info and a better word.”
So, “Elliot” is just some sounds we use to refer to a human being. That human being has never been the same thing as “Elliot” because all “Elliot” can ever be is linguistic shorthand for something that could never, ever be captured in language. (So yes, selfness absolutely transcends names.) “Elliot” is just a convenient shorthand that we use. It also matters a shit-ton that we use “Elliot” for that shorthand now and not a previous shorthand, because “Elliot” is what’s accurate. In particular, it’s what Elliot has told us is accurate.
Maybe the sounds “Ellen” used to be accurate, maybe not. Maybe Elliot was okay with having the sounds “Ellen” and all they convey used to describe him, maybe not. We don’t know him. All we do know is that it’s not accurate now. So, yeah, imo a polite person – especially a polite stranger – doesn’t mention the deadname because we have no idea about used to be accurate or what Elliot is okay with. We’d have to be Elliot’s friends to know that and we’re not, so.