The B3030 was/is a premium B as is the current B2650. The last two numbers designates the premium series which can change as the series numbers change.
/ Which B-series Kubotas are Considered "Premium" Models?
As of the last couple generations, models ending in 00 or 01 or 10 or 20 are not premium. The premium models have ended in 30, 40, 50, 60. Not sure if there is a real pattern or standard to it though.
/ Which B-series Kubotas are Considered "Premium" Models?
It's hard to tell as Kubota didn't have as clear a line between the premium and base model B's of that era but best I can tell the B24, 27 and 2910 were premium and the B7510 and 7610 were base.