I did not know that the window sticker on the 87 after Septeber was 87 1/2
From Wikipedia:
In 1986, a modified engine design with intercooling boosted the performance even further; in 1987 it reached 245 hp (183 kW) and 355 lb·ft (481 N·m) of torque. Buick dropped the T-Type package for Regal in 1987. There were only 7,896 Turbo Regals produced in 1986. In 1987, when Turbo Regals reached their peak in popularity, a total of 27,590 Turbo Regals were produced through December, with those models produced between September and December of that year window stickered as "1987½ Buick Grand National" vehicles.
From Wikipedia:
In 1986, a modified engine design with intercooling boosted the performance even further; in 1987 it reached 245 hp (183 kW) and 355 lb·ft (481 N·m) of torque. Buick dropped the T-Type package for Regal in 1987. There were only 7,896 Turbo Regals produced in 1986. In 1987, when Turbo Regals reached their peak in popularity, a total of 27,590 Turbo Regals were produced through December, with those models produced between September and December of that year window stickered as "1987½ Buick Grand National" vehicles.