Hello,
In fact, one way or another, virtually all of the characters depicted in the First Somerset Strikers sourcebook (and the BattleTech cartoon) have appeared in canon (except, IIRC, Valten Ryder). But the show took some extreme liberties with canon to reach its target audience, and the sourcebook's attempts to justify all of it kind of breaks down on close inspection. As a result, it is treated as an in-universe fictionalization of actual events.
The First Somerset Strikers, commanded by Adam Steiner did exist, as did Nicholai Mathus and his Falcon's Claws, and Franklin Sakamoto was even there, and really is Theodore Kurita's illegitimate son (in fact, we see his mom get murdered at Indrahar's request as early as Heir to the Dragon, way before the cartoon; we likewise see Ciro Ramirez as early as the first Blood of Kerensky novel, where he fails utterly to impress his classmate Victor Steiner-Davion). The 1st SS and the Claws did spar on numerous occasions during the early Clan invasion, but their path was likely somewhat different, especially with regards to the Camelot Command event, where the show depicts a radically incorrect version of the Clans' origins.
Hopefully, that helps.
Thank you,
- Herbert Beas
BattleTech
Catalyst Game Labs