February 1998... or?

Yep the frame is a 1998, specifically the serial number started with a J indicating 1998. The first two digits indicated the Year and Month for frames of this era.

YearMonth*

E=1993, F=1994, G=1995, H=1996, I=1997, J=1998, K=1999

A=January, B=Febuary(sic), C=March, D=April, E=May, F=June, G=July, H=August, I=September, J=October, K=November, L=December

The although mine initially looked like _5, after photographing it and running a few filters on the photo, I think it is JB. The vertical part of the J is hard to see, the same with the upper curve of the B.

The photos in a clock-wise direction starting with the top left photo are:

Original
Inverted
Black and White
No-idea, lots of filter setting applied.

Anyway for now the code looks like JB... making it Febuary 1998... or?

* Serial number information from Vintage Cannondale