Random shower thought:
Why didn’t GL change Obi-Wan’s line…
“You can’t win, Darth…” to “You can’t win, Vader…” ?
Why would he?
When Lucas wrote that line, Darth was his name. It made sense to call him Darth. But somewhere along the line, Darth became a title. Vader was his identifier, Darth was just a prefix.