Hello,
I must admit that here I honestly do not know. The descriptions in Field Manual: Lyran Alliance identify them as made up of FedCom Guards RCTs that were considered the "least loyal" to the Archon in the years after the Lyran secession, but I'm getting the impression you also read that passage. This may be one area where the author left things deliberately vague to minimize or avoid continuity issues. (We do that from time to time.)
Hopefully, that helps.
Thank you,
- Herbert Beas
BattleTech
Catalyst Game Labs