Went to the Mopar Spring Fling (Canada) show and asked about your trunk lid. Both "Gurus" said the same thing. Your trunk lid is a '72 and up version. The larger cutout is the same pattern as used on '71's for the Gull Wing spoiler. That one cutout was put there merely to facilitate the installation of the trunk light wire. One of the guys actually had your identical lid for sale there.
I was always curious about the one large cutout on those lids too. I'd be curios if your investigation comes up with the same. Sadly though, yours is definitely not a 1970 trunk lid, it had to have been switched out at some time.