Quality chart is outdated
I understand now, however I would think higher quality grades for carpentry would be named to differentiate between X grade and GM+master x grade. seems a little lacking.
The grade system is not just for carpentry, it's the same item quality system that the game uses for other things too (like cooking, blacksmithing, tailoring, even dropped weapons from monsters and synthesis). In addition what if somebody has the GM effect on but doesn't have carpentry as their active talent? Then they'd get those stats minus the third line.
So the bonuses are listed separately because they have separate sources.