I'll go with the most straightforward conclusion on the origins of the TDF; that it was a creation of the post 2933-era reforms that saw the organization of the ComStar Guards and Militia. It had no meaningful links to any old SLDF commands, but more likely was directly descended from the initial five light infantry regiments trained and equipped by order of Primus Hollings York.
Ok, my next part of the reports now starts with...
Part IV: A Distant Hope? Or a Hidden Nightmare?
With the successful conclusion of Operation Silver Shield in 2788, the whereabouts of many SLDF units that did not immediately flee the Inner Sphere with Kerensky or defect to the Great Houses was confirmed, if only for a brief moment. However, the sheer number of missing divisions and regiments from this period means that Silver Shield cannot account for all of them. Even if the ten divisions involved in some form with Silver Shield were directly analogous to former SLDF commands, that still leaves six other divisions and perhaps another half or dozen independent regiments unaccounted for; a significant military force.
And there could have been a significant number of other former SLDF commands to join the ranks of the above. Many "elements", possibly ranging in size from a single battalion to a whole brigade, of divisions disbanded by Kerensky after the end of the liberation of Terra are left accounted from. Some joined House armies, some probably sided with ComStar, but that leaves at least a dozen or more "elements" to join the ranks of the missing. Keep in mind the murky fates of other units from other SLDF commands like the Marine Corps, Special Forces, and Corp of Engineers as well, as they have to be considered as well.
So we have a force that numbers anywhere from 80 to 140 (or more) combat regiments plus supporting elements just floating around somewhere. Did they form into a cohesive group? Or did they scatter off bit by bit? That much is impossible to say. But what we do know is that even centuries later, small elements of the SLDF kept popping back up into the view of the Inner Sphere. Take the case of the Blackhearts, a former SLDF Special Operations Group that managed to stay off the radar for the better part of a century before reappearing during the start of the Third Succession War, piloting a whole regiment's worth of mechs. And is the 242nd Hussars mercenary regiment that is seen wandering the Periphery in the 3050's the descendants of the original Royal 242nd? Very likely. Even the Eridani Light Horse could have ended up like this; they spent several decades out in the Periphery trying to start a farming colony until pirate raids forced them back to the Inner Sphere to become mercs.
So say this "Hidden Army", this "Second Exodus Fleet" traveled out among the stars looking for a new home. What would have happened to them. Here are some theories:
1. They're dead, Jim. Depressing as it is to think about, the fate of many other SLDF units that tried to settle out in the great beyond suggests such a force could have died out for one reason or another. The original Exodus fleet came within a hair's breadth of exterminating itself less than two decades after it left the Inner Sphere, and it had resources on a level this theoretical second group could only dream of. But maybe that was due to a failure of imagination on the part of General Kerensky and his staff. If the Second Exodus had a small but driven group of leaders who set reasonable and attainable goals for the future, then they might not have had the severe social collapse of their brethren. Which leads up to...
2. They're okay, Jim. They set up shop somewhere out there, in a region of the Periphery that no one cares much to explore. Perhaps 200 or 300 light years beyond the Concordat, or in those vague regions out beyond Tortuga. Perhaps the decedents of the Second Exodus like it that way, and have no intention of changing it.
3. They're... no this joke is getting old. To expand on the above point, they might be alive and waiting for their chance to strike back at the Inner Sphere. They found a former Rim Worlds mech factory world or two, or a deep space SL colony like Niops, or on a smaller scale Columbus. With a halfway pleasant world to settle down on, and an industrial infrastructure to build upon, they are busy painstakingly rebuilding the old SLDF back to its 2750 levels and will then use it to beat down the minions of the Third (False) Star League sometime around 3350. Taiw...St. Ives will rejoice.
4. Somewhat less tongue-in-cheek than above, they managed to bump into a proto or micro-state out in the Deep Periphery, and found themselves a decent new home worth protecting. Or maybe a repressive dictatorship that needed a hardcore thrashing. Anyway, they merge and rebuild with this new state, like the Ghost Bears did with Rasalhague or the Snow Ravens did with the Outworlds Alliance or the Goliath Sc... Boy, a lot of those Clans like merging with other per-existing states don't they? Just throwing that out there.
Merging with another nation of people would present interesting challenges for the Second Exodus, and could go down in any number of ways. Do they successfully impose an elite SLDF-style military on their new comrades, or do they "go native" and adopt the military practices of their new brothers? Did this micro-state have Battlemechs before hand, if even in small quantities, or did the Second Exodus just introduce the "fire stick" to a legion of innocents. Maybe the Star League officers become a new ruling class over the alien masses, like the Greeks in Central Asia in Antiquity, the Norman knights in England, Palestine, or Sicily during the Medieval period, or Babur and his men in India during the 1500's. They introduce Star League culture and technology to a less advanced but productive people, and a new hybrid civilization flourishes from it...
Or they all shovel horse dung to keep the fields alive.
A lot of possibilities here. Any other questions or comments? Thank you so much for following my ramblings, I hope to have something else to needlessly over-analyze and pick apart soon.