I've had this penny. I've looked it up. And read about it. Now I'm seeing if it is truly the floating roof!
In the Cherrypickers' Guide, there is a 1969-D with missing designer's initials variety. The book says the missing initials are from over polishing of the die. The floating roof, the missing part of Lincoln's coat are most likely from the same type of overzealous polishing.
In my humble opinion its not the same coin as the pics you provided. If you look closely at the pics of the actual error coin you will notice that it has fully struck steps in the lincoln memorial and has most of the details it should like lincolns statue between the poles. Over polishing only removes devices in the polished areas like the mint mark and lincolns coat. The coin you found appears to have been either a weak strike or more then likely struck through grease but im certainly no expert and could always be wrong.
But getting your hopes up is all the fun! If you keep searching you will find something big eventually, it just might take a life time. Cherry picking unattributed variety's already slabbed is what I liked better because you dont have to search coins till your fingers are black.
