It looks like there is an 8.H behind the TANGE stamp, which indicates August 1988. That's right in the grey region where it could be a 1988 or 1989 model. I thought the Japanese would be even more demanding of amentities than the USA market but it appears not to be the case. Many Tange CrMo double butted tubesets used a seat tube with a 28.8mm inner diameter, including #1, #2, #3, 900 and Infinity. Many manufacturers would use a 26.6mm post with these sets but if a light reaming operation was performed, 26.8mm would be appropriate. This is exactly what I was expecting and, as I stated, it doesn't help much because this size was used on so many Tange tubesets..