the s1 b16 tranny is 90-91 so you were told correct, you have to return it an get a 91 clutch. the 91 tranny has less splines on the input shaft than the 92+ trannies, and the clutch friction area is 3mm wider on the 92+ so it has more friction/contact area on the flywheel.
a quick search online for your s1 tranny spec could of saved you the trouble and the $20 refference fee from nice people 