I'm no expert on this but I have several sets of green tip limbs and several sets of the modern FF limbs and have been shooting the Bear t/d for several years now. Following is what my understanding is; I do know that the 2B does not mean that the limb is a #2 limb. The green tip limbs were marked for the B riser. Reason, I guess, is that the A riser was only made in '69 through '71, along with the original B risers.
Production of those bows stopped when the compound bow hit the scene in the early '70's.
Bear continued with the production of the magnesium risers in the '70's but I'm not sure which color tip limbs were made with those risers, my guess would be the red and/or white tip limbs.
The green tip limbs that you speak of, were made when the Green stripe B handle came back in production somewhere in the early '80's; but only the B handled, not the A. Therefore, the limbs were marked for a B handle; the 2B that you speak of is just part of a serial number marking. If a green tip is marked 60" then that is a #1 limb; 62" would be a #2 and 64" would be a #3.
The A handle came back in production, my guess, is in the late '90's along with the modern FF limbs and newer B handles. Those FF limbs are marked with lengths and poundages for both A and B handles.
Hope this kinda helps.