Rather admitted that his account of what he saw was wrong, that he had given a rushed description. He said he saw the film once - Zapruder projected it onto the back wall of his office - and rushed out with no notes to broadcast what he saw. And it wasn't a copy of the film; it was the original.
Here is Rather in his memoirs: "The lawyer [Sam Passman, Zapruder's lawyer] laid out the ground rules for us: He had set up a projector in a private room. You went in, looked at the film one time, took no notes, came out and gave him your bid. I was already saying to myself, the bid comes second. The first thing I am going to do is look at the film, then knock the hinges off the door getting back to the station and describe what I had just seen. Then, and only then, would we get into the bidding."
And this (from Alexandra Zapruder's book): For his part, Rather defends his misrepresentation of what was on the film not by acknowledging that it was irresponsible to give an account after having seen it only once, but as follows: “At the risk of sounding too defensive, I challenge anyone to watch for the first time a twenty-two-second film [sic] of devastating impact, run several blocks, then describe what they had seen in its entirety, without notes. Perhaps someone can do so better than I did that day. I only know that I did it as well and as honestly as I could under the conditions."
Of course none of this matters. The same folks will repeat the same groundless claims and then demand their claims be proven wrong. When they are, they will ignore it and then repeat the claim. More than 60 years of this.