That's what I think too. Besides, as a general rule, we usually maintain titles and ranks which are associated with a specific position or group ("Invader" for Irken agents; "Almighty Tallest" for their emperors; "Darth" for the Sith; etc.).
You know, the Irken title conventions have never been explained in detail, since the only canonical emperors are simply Almighty Tallest Red and Almighty Tallest Purple. It's strange (although not impossible) to think that "Red" and "Purple" are birth names and that, had they not been emperors, they could have been "Invader Red" and "Invader Purple". Could they be twins who only received these names because the only difference between them is their eye color? It's very sad that the canonical status of Almighty Tallest Miyuki and Almighty Tallest Spork are up for debate, although I hold some hope that perhaps Enter the Florpus! will finally show them in flashback, possibly.
As for the Sith, I agree that the birth names takes precedence over the Sith name in the gallery, not to mention the rare instances of former Sith, such as Maul.