Last number in '90 is 1099, it's a '90 . At the time Guild only called it "Sunburst", see the label. The bursts in the mid-late '90's tended to show more red at the edges, very close to a "Cherry Sunburst" which was actually used at times. I like those lighter-edged bursts myself.
Stamps were normally on the treble side bevel on the neckblock, hard to see unless you know you're looking for it.
"SB" on label just means "Sun(B)urst", that's what they called it.
Also be aware that I think I've seen more s/n chart errors/omissions in that particular era, '87-'93, on that particular series (JF30's and JF30-12's), than any other period/model, not sure why. Suspect it my have something to do with the sale to US Music Corp and paperwork disarray.
JF30's like F50's have 17" lower bout and at times were the only 17" maple archback F-body in the catalog according to price lists of the era ('87-'93).