it has a four digit serial number 8912. I believe it was manufactured in the 1980's
That would be an 89 J-6 made in Japan. Nice!.

Stop. Engage brain.
If your surmise were to be valid, then clearly there were a mere 100 guitars made in 1989 at that plant -- like, s/n 8900 - 8999.
Must be worth a few thousand $$$, considering that scarcity.

It's little better to guess that the leading digit indicates 1988, because that means 1,000 could be built (8000 - 8999). I'm only guessing, but it seems to me that Washburn coulda sold that many just to the fans in downtown Tokyo.
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Until rather recently, serial numbers WERE NOT some sort of secret code. They merely tracked each guitar as it was completed, which is to say in a
serial fashion. Until 1976, that's how Fender instruments were numbered (with some odd glitches).
Some companies used various leading digits or prefixes in order to indicate different plants, assembly lines, shifts, design changes, etc. This is exactly why early Washburn (Lyon & Healy) instruments seem so chaotic nowadays.
So, a recent Fender with a leading M is a Standard (made in Mexico), the next letter indicates the decade, & the next digit gives the year of that decade. The remaining digits are nothing but the next available number when the guitar passed inspection. And FWIW, realize that those serial numbers are 8 or 9 characters long, leaving room for (respectively) 100,000 or 1,000,000 units per year.