Old mate has it built on the 7/1990.....which would make it a 1990 or even a 1991 model.
I wonder were he got that date from,Pretty sure Yams of this era only had a VIN ,No build date except for the rims maybe,perhaps compliance plated
I seem to recall them bringing out a limited run of plated ones in the WR version if it is one
, I think they may have had a lighting coil too