mamiya 67 lens designations

Help....just won an rz67 with a 65mm NB lens....i thought it was a recent lens but seems it is an older one...could someone explain FAST....prefer newer lenses......want to make sure what i would be getting....thanks for your help. I understand non C and C and KL but where did the 'new barrel' fit in the line?
richard

NB is a non-C with a differently shaped barrel.

Also, if you have an RZ67 body, you don't get full functionality with an RB67 lens. I'm not sure exactly what that is, because I've got an RB67 not an RZ67.

The newest, fanciest, fastest lenses are the KL series. Generally the non-C, NB, and C lenses are the same speed, just the C lenses have better coatings.

RB lenses won't focus as close on a RZ. I think they also might not handle the auto mode on the metering prisms that well.