Yes, the understanding is that trans people were always trans. It may have taken time for them to understand that and perhaps more to decide to adopt that identity publicly, but they're not "not trans" before that. Other queer identities are generally thought of the same way in queer communities: many people have early experiences (e.g. fixating on same-sex characters in fiction the way peers might opposite-sex characters) that they later realise were early expressions of their orientation.