Ok, a slightly more descriptive summary here: the introduction is signed as being written by paladin Contsance McGuire in 3150. The sidebar, which it not dated, only signed by lore master Stephan Roshak and addressed to the ilKahn, does mention motion that the 'original document', referring to the intro and the book as a whole, are a draft that was written over a century ago. That draft was, 'made available' by the exarch, it was 'discovered' by gunslinger Eli Sender. Furthermore, it notes that, while the document (the 2SW book) is old, it may make a useful reference for sibkos of the history of the inner sphere 'during our exile'. Now, I assume that to mean the original exile of the SLDF, since that is when much of 2SW happens.
That bit about the exile, and the fact that 3150 is pretty much a century after that exile ended, threw me, and made me question whether the sidebar to the ilKahn was 3150 or 3250. Reading it again, I believe the sidebar is written in 3250-ish.
Also, I read through the intro story about the death of Jerome Blake and the beginning of Comstar as we knew it in 3SW. It is a complicated piece with a number of details, and I don't want to paraphrase it here because I would honestly be giving you my opinion of what it meant, when you might not agree with me after reading it yourself. What I can say, unequivocally, is that Jerome Blake died peacefully and that Conrad Toyama predicted they might name a BattleMech after him (him being Toyama, not Blake.) Actually, he thought it might be a BattleMech or a Warship, but I think between the two, he would be more pleased with the Mech than the Warship.
Anyway, for me, the intro fiction alone was worth the price of admission. It isn't Earth shattering, but I think it is a very honest explanation of a longstanding mystery. Now, on to the destruction! At least until I fall asleep.
EDIT: also, I think there is an error in the "weapons and ammo" box for the Thunderbolt on p.117. The stat box on p.116 says that both variants have an ER Large, 3 Mediums, and two Small Pulses, and that the -5L has an LRM15 with Artemis IV and a streak 2, while the -5LS has a standard LRM15 and standard SRM2. The weapons and ammo box on 117 says they both have an ER Large, a standard LRM15, 3 mediums, and 2 small pulses, while the -5L has an additional ER Large and Streak2 (plus CASE) and the -5LS has only an additional standard SRM2. I'm pretty sure, of the two, the stat box on 116 is right and the weapons and ammo box on 117 is wrong.