...I believe the FBI is also capable of determining when, where and by whom a paper was made and how old that particular sheet of paper is, which businesses and government agencies ordered/used that type of paper, etc. I also believe they have vast resources permitting them to identify the properties of inks used in things like pens... and typewriter ribbons.
B, they will not get an original, just this copy of a copy of a copy from what I see.
They can only go by the typewriters of that time and maybe office inventory lists of what they had.
In addition, having a retired man still writing official documents for the government a year after he was gone from there is absolute proof of fraud right there IMO!
As far as how far they can go, if they wanted to say there were carbon paper copies and other copies, all they have to do to reproduce that is to again use word, plus ONE other step.
They would then use a pin printer to do the memos and make the carbons.
They could date the carbons if they exist though!!!!