It was a "short" spoiler, and I've since learned that my car would've had one (if it were a true D80 car) since it's an 02D build. But I've already got the "long" spoiler painted and mounted to appear "dealer installed"
Not exactly true. Both spoilers were used in production starting 01B, continuing at least through the end of February.
The full-width '69 rear spoiler entered production 01B as evidenced by the July '69 SS&DI road test of Olympic Gold Yenko N579281. It is pictured next to the Yenko Chev house race car N578713, also equipped with the '69 rear spoiler. The August '69 HP Cars road test of ZL1 #3 N608193 [02D] shows it was built with a '68 rear spoiler.
Z11 production at Norwood began 02D and I am not aware of any built with a '68 rear spoiler.
It's my understanding that rear spoilers were received at the plants painted and could not be returned as service parts. Existing stock at both plants had to be consumed in production.