Hee hee...What is this weird point you keep pushing? Every second post is about people not knowing "Vader". wt...?
You mean, how Sidious just said "you will be known as Darth...Vader"?
...or how Yoda said "consumed by Darth Vader"?
Who knows...never bothered me though. Yoda probably just figured it out through the force.
Or maybe how this whole Darth/Sith thing works is that the spirits or beings of these various "Darths" have just been kinda floating around for eons until people give into the dark side enough and become embodied by them...like demons or something. So, Darth Sidious himself was actually just some normal dude that at one point got consumed by the Sith spirit "Sidious".
Who cares if it's not explained...it's kinda cool not knowing. Doesn't have any effect on the movie/storyline.
...honestly, I personally don't know and don't care much of what's outside the movies... kinda make a point of it.