Given the number and caliber of changes snuck in in various places by various authors (LKW, Doug Berry, Chris Thrash, Steve Bloo, MJD, etc) either by design or accident, the GTU diverges in many ways from the OTU, in some cases simply by defining things previously optional (or even non-defined at all) as default.
There were lots and lots and lots of details about the OTU that was undefined at the time the first word about the GTU was written, but except for Foreven Sector, I'm not aware of anything that was optional (Well, it's
all optional, of course, but I don't suppose that's what you mean). There may have been some, but mostly there were gaping holes that no one had gotten around to defining yet. As Robert Prior so wisely said a while back:
"The very act of writing a Traveller book closes the doors on possibilities. Any game supplement does that, assuming the publisher cares about internal consistency."
So many forget that even just pinning down one of several prior options is a significant change.
Not I. But I consider that a feature of new material, not a bug. If the new material happens to overwrite something I've already covered myself IMTU, I'll keep thing the way I've already told my players IMTU. Nothing forces me to adopt any new facts if I don't want to. If (as is often the case) the new material fills in one of the huge number of holes IMTU, I'll grab it with loud hosannas and use it to fill out another bit of my TU. So to me new material is at worst "No effect" and most of the time it's a bonus.
Loren's big one (and Doug's, as well) was that all IM's are BD trained; that runs counter to the CGen tables, in both CT and MT.
I gave Doug a hard time about that at first, but he pointed out that although it certainly is a change, it's one that goes back to CT material. It showed up in Loren's writeup of Imperial Marines in JTAS #12. The MT authors should really have changed the rules to reflect that
. After all, they had two conflicting bit of canon: Basic rules that applied to every generic marine in Charted Space and a specific description of one specific organization. It seems to me that the specific is stronger evidence than the generic.
In any case, even if it had been a genuine discrepancy, you can hardly say that it's such a big difference that it outweighs all the similarities between the two universes.
(Just to be clear: I think Loren made a mistake when he established that all Imperial Marines were BD trained, because it makes them less useful to a GM. There was a quote somewhere in GF to the effect that "The moment the Marines arrive, the battle is over". Which means that as a GM, I can't really allow the Marines to arrive and spoil the fun. But there's no doubt in my mind that he did establish it and that that's the way it is in the OTU (And the GTU.)
Hans