Everything that is explicitly stated in a G-Canon source is G-Canon and nothing else, the rest lies in a lower level of canon. A good example is the group of bounty hunters Darth Vader mandates to find the Millennium Falcon.
They are all named in the Script
The group standing before Vader is a bizarre array of
galactic fortune hunters: There is Bossk, a slimy, tentacled
monster with two huge, bloodshot eyes in a soft baggy face;
Zuckuss and Dengar, two battle-scarred, mangy human types;
IG-88, a battered, tarnished chrome war droid; and Boba Fett,
a man in a weapon-covered armored space suit.
VADER: ...there will be a substantial reward for the one who finds
the Millennium Falcon. You are free to use any methods necessary, but
I want them alive. No disintegrations.
So their names and appearances are all G-level, but not their back stories.
From Canon article on Wookieepedia :
G, T, C and S together form the overall Star Wars continuity. Each ascending level typically overrides the lower ones; for example, Boba Fett's back story was radically altered with the release of Star Wars Episode II: Attack of the Clones, forcing the retcon of older source material to fall in line with the new G-canon back story. However, this is not always absolute, and the resolution of all contradictions is handled on a case-by-case basis.