T-Mar,Just discovered this thread (after reading the one on the Steve Bauer Mystery Bike), and I'm intrigued. I have several SB's, so I tried to confirm their dates of manufacture using their serial numbers. Not sure the guide works for them, though. Like the gentleman up-thread with the SB Whistler, mine have SN's that start with two capital letters, followed by 5 numbers. That doesn't seem to fit the Yamaguchi system suggested for them, as it starts out with letter-number-letter. The ones that do appear to correspond (during the mid-80's) to the SB sequence look to be those of Fuji, Kawamura, Maruishi, Miyata and Tsunoda - but of them, only Maruishi's produced dates that make sense.
Specifically, mine have SN's that start with either F (like both the Whistler's and the SB Mystery Bike's) or G; followed by either H, N or S. Assuming the second letter refers to a fortnight, Mariushi's system would give them dates ranging from April '86 to April '87 - certainly a period compatible with their colour schemes. Do you think Maruishi could have been the (or a) builder of early SB frames? Or have I muffed something? Thanks so much, BTW, for putting together and sharing all this info!