The Hohner site used to contain, quite a few years ago, a chronology of the models produced, that showed the B2 bass as introduced in 1985 and the active fretless version B2AFL a year later, in 1986. There was no mention here of the B2A, which may well have appeared in 1985 along with the passive version.
They were produced until 1993 in their first batch, then reintroduced probably near the end of the 90's, and all of these were manufactured in Korea by Cort.
The Jack bass, also licensed by Steinberger, appeared in 1988, again according to this document.
I don't know how that chronology is reliable, but it makes sense to think that the first two digits refer to the year of production, even considering the evolution of the B2 series. I collected the information of around 15 basses of this early production (I personally had four of them) and all had serial numbers starting with 86 to 90.