The expert was suspicious about the proportional font, but consider this: wouldn't that be the first thing anyone would notice? How smart would it be for CBS to present a document that couldn't possibly be typed in 1972?
Don't answer that.
How smart would it be for a forger to produce an impossible document that sticks out like a sore thumb, especially when ordinary military typewriters are easily available?
I respect the expert's opinion, particularly when he gets into the nuts and bolts of typeface differences. This is enough to require a look at the original document.
It would be stupid. But the lamestream press is so used to for years working on "Gentleman's agreement" wink-and-a-nod basis, in which no journalist DARES to criticize a "colleague that anything is acceptable.