Okay, this is informative. Because the Audubon on the cover says No. 804, the booklet was issued after 1990 or so. Immersion testing would only be done to assure waterproofness, which is what makes the model so expensive. The designation B191 indicates the Japanese company that put the final product together, Seiwa Optical Co., Ltd., Wako-Shi. That company also made other models, such as the Nighthawk series in the 1970s and 80s.
There really isn't too much more to discover except how the instrument performs.
Ed