I did a little research. Apparently for the 1988 model year, you could order factory ground effects on any model regal. In 1989 the ground effects were only available as part of the GS package which was added sometime during the 89 model year. All of the GS options (wheels, suspension, ground effects, etc...) were available in 88, you just had to purchase them individually.
Since you bought your car at the very end of 1988 and it was titled as an 89, it is probably one of the last cars built with ground effects that was not also badged as a GS. I think a regal limited with ground effects would be a particularly rare car.
Very interesting !!
