this is because in 1989 G plate was year they swaped onto 90 spec big bumper +electrics...Aug 1989 was last of small bumpers on old spec electrics...
so speaking no such a thing as 90 spec mk2's as its changed over in 1989...90 spec is just the last of the mk2's as vw where working on the mk3 being brought in..
personaly always preferd small bumper mk2's even though i drive a 1991 gti

....but moving house soon ..and plan to buy another small bumper valver

...and make current mk2 into a daily