Have been looking into this in some free time since you posted. Not allot of people/owners taking pictures of this panel and that lower corner is hidden from view on an fully assembled car.
What I've found so far.
All of the 69's I've found pictures of so far with fold downs had the notch in the lower corner at the trap door opening.
Pictures are from different cars. Do have more of this version
Did find corner panels as you show but the pictures are not labeled to identify plant they came from. Given the paint finish on the panels should confirm they are 70's
Unfortunately this does not address your fit issue. Still hope this helps