I'm not biblical scholar, but I do know something about this issue of the Psalm numberings. The Greek Septuagint numbering is the numbering that the Douay-Rheims uses, for it translates from the Latin Vulgate, which also uses the same numbering. The Hebrew numbering is actually from a later Hebrew text called the Masoretic text, which is the one that the Jєωs and Protestants use. The Greek Septuagint has the same numbering as the original Hebrew text. So the Douay-Rheims translation has the correct numbering. Now, in the Novus Ordo, the Masoretic numbering would be used in the New American Bible.