That's quite difference, one extra letter and two numerals dropped. No wonder, the originally reported S/N didn't make sense. The latest version indicates that the frame was built in December 1987, That's late enough the calendar year that it should be a 1988 model. However, a 1988 model should have Shimano 600 Ultegra, as opposed to the previous generation New 600EX. This suggests a rebuild which would be corroborated by the March 1986 date code on the front derailleur, as previously noted by garryg.