I am not sure what to think. If it should have been c instead of d the forger made an amateurish mistake or else the original copy was changed. I would think they at least had a BC of the ERA to copy...so until I see one I am in limbo...but not holding my breath. As we all knew the key was to check the books and page and probably everything near it! I don’t know maybe the official printer made a mistake, wouldn’t be the first time! Need something to compare with right now...
It is an old typewriter with a cloth ribbon that probably had build up on the 7 but not on 6 or d. Also with non-electric typewriters some typists are weak on some letters/numbers while hit stronger on others.
My Mom had one of the old typewriters.