Adjuchas and Vasto Lorde 

You are right, nothing official was said.
But, thinking like this, we would say Arankaru and not Arrancar, right? But we use Arrancar because that's a word.
The same goes to Adjuchas and Vasto Lorde. Adjuchas I can't recall precisely now, but is a kind of monster similar to the illustration we saw when Hitsugaya talked about the Ajuukasu. About Vasto Lorde, as you ar aware, means "Vast Lord" in English.
I choose the spanish romanization because, if it was Vast Lord, the word wouldn't be vastoroode, but vastoroodo.
I just changed the names because I know we are always trying to use the real words instead of the raw kana reading. And Adjuchas and Vasto Lorde are the only "real" romanization I ever saw to Ajuukasu and Vastoroodo. -