I could have produced this hash at any point in the past, but after HN's edit window expires, one can be very certain I did not originally produce it at any point after the timestamp. This is far from useless, even if it doesn't cover all possible objections. The objection in the original comment that it does cover is: you just made up this footage/other evidence post-hoc to establish an alibi now that you've been accused, as people frequently do, or you can't prove you didn't make it up post-hoc so we want to get it tossed out as non-reliable.