Was looking over at "Four Eyed Pride" the other day and it would appear that FEP site administrator "FoxChassis" has cracked the secret of identifying bi-wing delete cars via buck tag stampings. This is the info you would find on your buck tag:
11 (SVO only) = hatch w/ defrost & single wing spoiler
12 (SVO only) = hatch w/ defrost & bi-wing spoiler
Now, i'm no expert on BWD cars, but his seems to be the first firm proof on how to id a car without all the original paperwork.