A scientific linguistic description of the grammatical categories of Middle Maithili based on new archival evidence culled from Newari MSS. of medieval Maithili literary texts stored and preserved in the Nepāla Rāṣtṭriya Abhilekhālaya in Kathmandu is, to my mind, a necessary and indispensable prerequisite to legitimately authenticate the historicity of the growth and formation of the Maithili language and literature. This paper essays to present a historical linguistic description of the auxiliary verb forms attested to in a total of 14 Newari MSS. of archival literary works of Middle Maithili (9 Dramas & 5 Songs) composed by the Newari–speaking royal men of letters of the Nepālamaṇḍala and published across the globe during 1891–2024 CE spanning a total of 133 years. It is hoped that this historical linguistic analysis will help ascertain some new archival evidence for the textual history of the Middle Maithili auxiliary verb forms; it may also help establish linkages with the contemporary usages of auxiliary verb forms in Modern Maithili.