The following article provides a critical edition and analysis of a Dunhuang Tibetan version of the Mañjuśrivihārasūtra (Tib. 'jam dpal gnas pa'i mdo) as a case study for documenting the historical development of Tibetan translations of Mahāyāna sūtras. The critical edition of the Dunhuang Tibetan version is based on one complete Dunhuang manuscript as well as four Dunhuang fragments, three previously unidentified, to restore a Tibetan version of the sutra that existed before the imperially decreed (bkas bcad) language reforms of 814 c.e. The critical edition is annotated against seventeen Kanjur editions of the sutra, including Western Tibetan manuscript Kanjurs (Tib. bka' 'gyur) from Basgo and Hemis that have not been previously investigated. The Kanjur annotations document the revisions that Tibetan editors made in implementing the codified rules and principles for translating Buddhist texts issued by Khri Ide srong btsan (r. 800-815 c.e.). In addition, the annotations provide evidence for three lines of textual transmission, the Them-spangs-ma group, Tshal-pa group, and a Western Tibet group. The documentation of the variant readings has also been supplemented with computer-based phylogenetic systematics to discern a refined estimation of the genealogical relations among extant textual witnesses.