This is a very nice set! I may be way off here, but for some reason 1981 comes to mind. That was the year the LB1 and LB5 were introduced, according to Dale Vincent's research found on AAPK. It was also the year before the LB3 came out, which would have been a logical member to this set if it were released after the LB3 was released. Again, this supposition is based on often faulty memory.