Weird... the pics aren't showing up for me...
Probably my (slow) work connection, not JNC...
For the record, I confirm I searched '71 and '72 parts catalogs and while there was a listed part number for the rear over-fenders of a KPGC10 coupe - there were no added body parts listed in either catalog. That means no chin spoiler, no trunk spoiler, no front over-fenders. Heck there were no over-fenders listed for 4 doors either.
I've seen pictures of genuine rear over-fenders and they do have the Nissan part number labeled inside.
Rubber Soul currently sells two spoilers, one with the "SKYLINE" all caps on the underside for 27000yen, and one without for 23000yen.
Victory50 sells apparently exactly the same rear spoiler with "SKYLINE" all caps for 36000yen - no reason given why it's almost 10000yen more...
Both of the ones WITH the all caps are described as being factory correct repros.
For the cars whose spoilers look like they dip down in the middle - ie spoiler center section actually touches trunk lid - I believe that's a function of them having been mounted too far forward on the trunk lid. All the pics I've collected off the net over the years show a relatively set back spoiler with a clear gap between it and the trunk lid.
As Jeff mentioned above, I believe that the rear spoiler was solely a Nissan Sports Option - which presumably could be optionally dealer installed for a street registered car if the owner chose to have that done. I've found dealer sales brochure pictures showing street GT-Rs WITH the rear wing - thus the opinion that it was dealer installed.