Brigid, sister in Christ: Joy of the Feast to you!
I'm preparing to leave for church, so one quick answer before I do.
The Orthodox Church includes David's 151st Psalm in its OT canon of Scripture, even though the 151st Psalm is not used liturgically. THe 151st Psalm is generally printed in Orthodox Psalters. The Latins generally ignore this Psalm altogether.
The Septuagint version of the OT, which is the official version used by the Orthodox Church, does include more than the Latin Vulgate, which was originally based on the Septuagint, but seems to have been somehow influenced by the NT Hebrew version since the time of Blessed Jerome, if I'm not mistaken, and is somewhat shorter.