From the very helpful but admittedly incomplete sarna.net I proceed back to the Star League Sourcebook upon which so much of Field Manual Terran Republic 2785 was based. I'll be going over the SLDF deployment listings and distilling down all relevant data. Each SLDF unit as you know is listed in the following five times frames - 2764 (before the Uprising), 2765 (during the Uprising), 2766 (the Amaris Coup), 2767-2779 (Star League Civil War), 2784 (Exodus). Of course, I will be concentrating on the last one and already I think there is an interesting result. Certain units are listed to have survived 2767-2779 with heavy losses and then in 2784 are listed as disbanded. I think this backs my contention that Star League forces who took part in the Exodus were at or near full strength (90% or more of their command staffed and ready for action). Kerensky as a fervent Star League loyalist was no doubt trying to restore every command that survived the war despite those which took heavy losses but were still intact (20% to 30%). His plan to depart in 2784 changed those foolishly idealistic notions to disbanding those damaged commands and folding them into to existing ones who were brought up to near full strength. No doubt the reaction of the Houses to the initial departure (abject fear) of this huge fighting force is proof of this too. Of course I lack definitive evidence thus far. Just my initial conclusions on the 1st Army, posted below.
Just a few quick comments-
I agree that most of the SLDF units in the Exodus were probably at or near to full strength- and the canon material supports this.
As a general note from the 4th Succession War Atlas Vol 2 - P. 97 Dr Banzai explains what it means when he says a unit was destroyed:
When I say a regiment was destroyed, I was saying that the regiment had suffered so many losses, be it to their soldiers or equipment, that is ceased to exist as a cohesive fighting force. Seldom during the war did an entire regiment die to the last warrior. Some of the most devastating losses were suffered by the Fifth Syrtis Fusiliers RCT, whose various regiments lost all of their fighting capacity, but 30 percent of its soldiers were later rescued by the Federated Suns.
Given that the SLSB was written around the same time I would suspect a similar logic was used- with the exception of the SLDF units fighting the periphery that were nuked by the rebels- they probably suffered near 100% losses.
But you say that's an older source and does not directly refer to the SLDF, but rather the 4th SW and things may not be the same. In that case I direct your attention to First SW SB P. 14- the Hidden Agendas sidebar
Elements of eighteen divisions and a similar number of independent regiments chose to side with Blake. From this force, Hayes assembled eight full divisions with a similar quantity of reserve material.
So from 18 Divisions and 14 independant regiments, they were able to form 8 full Divisions.
As I was looking up information for this i just found the proof that units on the exodus were at near full strength.
From Liberation of Terra Vol 2 p. 114 it clearly says that "the force that departed with Kerensky still featured around a thousand regiments"
If each Division (Battlemech or Infantry) has 9 regiments then the 108 divisions had a total of 972 regiments. Add in the 63 independent regiments and you have 1035 regiments.
Further evidence that the SLDF forces were at full strength can also been see in the statement that the houses gained control of 128 regiments after the fall of the SL. The listing for the forces joining the houses/becoming mercs, specifically says that in many cases only 1 or 2 regiments from a division joined the houses. There is no such note for the forces on the exodus.