it remains the strongest candidate for an alien radio transmission ever detected
As far as I can tell, the signal was printed out on a piece of paper, and interpreted by one person, Jerry R. Ehman, who wrote "Wow!" on the printout, in red pen. In this interview, Ehman claims they had just one megabyte of storage. If the digital data remained stored to be revisited later after being printed, or if it was copied onto external storage, he does not mention that.
I have no reason to doubt dr. Ehman's integrity. But, it seems to me, had he wanted to, with a simple typewriter, he could have added a fake signal to the printout.
Is there evidence to the contrary?