As I said, hans, some interesting connundra. If pressed, I'd go with the T4 answers in most cases, which for the most part, are similar to CT.
For my own use, MT rules trumps all. For setting, CT and MT. My attitude on TNE and Virus has, if anything, gotten less accepting of it over the years... especially Regency Sourcebook.
But, in CT, MT, and T4, Nobles exist as agents of the imperium and/or individuals rewarded BY the imperium. MT had an apparent soc and real soc hidden in the rules (Your real soc didn't drop by non-payment of upkeep, and your apparent soc going to 11+ didn't make you a noble).
In any case, it is clear that these are Imperial Nobles for Imperial characters, Zhodani Culate nobles for Zhodani, Aslani Nobles for Aslan, etc...
CT also provides that nobles may have feifs . Enfeoffed individuals derive support from same, and some have Huscarles.
I rationalized that the best place for them IMTU was running the interstellar affairs. Which just happened to match up with much published canon.
GURPS traveller, 1st off, has made numerous cumulative dissonances with canon travellers, some as part of its premise, some as part of Loren's view, some (in part) as a result of persons frustrated by MWM failing to make in T4 changes they'd argued for for years... but by becoming authors for GT, they could impose them on the GTU.
mind you, MTU is no less divergent from the OTU than the GTU, but in many very different directions.
And, J4: CT, TNE, T4: 40% for fuel at normal TL's
MT: 25% at normal TL's, less at very high TL's
Maneuver:
CT: not defined, function is identical to MT core rules Reactionless Thruster.
MT, T4: Reactionless thrusters
TNE: HEPlaR
MT, TNE, T4: all have numerous additional thrust systems available. T4 includes HEPlaR. MT has a Fusion Rocket not dissimilar to HEPlaR, but without the technobabble. In all three one can mount multiple maneuver types, too.
But aside from the non-imperially-centered TNE, all the other three clearly provide for Nobles being specific to the Imperial nobility in the rules and in the "fill" texts.