Judging by the border on the settlement maps in TTA on pg 15, Gazulin subsector was not settled in 300 and was definitely settled by 400.
According to the information in MgT's Aslan and Trojan Reach books, summarized at
http://wiki.travellerrpg.com/Neumann_(world), Neumann was settled by Terrans. Not Solomani, but Terrans.
IMTU The expedition that settled Neumann had been a sub-light colony project in 2058 A.D., or -2460 Imperial, before the discovery of the Jump Drive in the year 2087 A.D. (–2431 Imperial), fully 256 years before the Rule of Man.
Using an experimental NAFAL (not as fast as light) drive capable of 0.35 meters per second acceleration, it took 51 weeks to achieve 0.355 light speed. Traveling in extended hibernation, they woke every 50 years to recover from the effects of coldsleep and to do what maintenance the robots were incapable of. It took 1,601 years for the colonists to make the 169-parsec crossing, of which only 1,508 years were perceived, and another 51 weeks of decelerating. First landing was in –856 Imperial.
Using the Species Lifespan portion of T5 I came up with a progression from TL 8 to TL F nearly TL G and with that rough placed the disaster at ~ 324 Imperial. At this point, I'm wondering when scouts of the Third Imperium came across Neumann. At that time the Imperium was ~ TL C If they found it before 324 then they were faced with a much more advanced civilization if only 1 (Planet? System?) and after 324 Not only were they still more advanced at TL D even though they had regressed some, they also had that nasty ongoing nanite problem going on.
I would postulate that the Scouts would have Red Zoned the planet/system until some way of "sterilizing" could be found to keep the nanites contained.
I think that point would have been around the time that the Imperium achieved TL F. At that point a Navy Base was established to ensure quarantine procedures were met, the Red Zone removed and the planet was inducted into the Imperium. Although from the MgT write up I'd still expect the planet to be an Amber Zone.
Does any of this make sense or am I way off the deep end? From CT adventure 1 I believe that the Imperium had TL F available around 1074 at least. Any thoughts, comments, skewers?