After the New Colony Region was formed by the Canopians and Taurians, ca. 3056.
Pardon the old thread bump...
This is correct. They were formed as an organized command as a result of the Treaty of Taurus circa 3056. The Taurians equipped them, including the development of the Marshal and Anubis Battlemechs, and the Canopians trained them on Detroit. The Marshal MHL6-FR (Fronc Reaches) is an all energy platform specifically designed to enable zero ammunition dependency on prolonged solo missions.
They are organized in both unit sizes as well as single individuals.
An Errant is different. They are lone mechwarriors usually said to be in old, dilapidated 'Mechs that are hired to defend remote, isolated settlements and colonies. From my understanding they were unaffiliated with any larger nations or command, but I imagine that could differ.