There's so much we don't know about Ancient History. Do you know how gladiators would say, "Those who are about to die salute you!"? Well, they didn't. Or at least, we don't know if they did. There's one time in history where anyone was reported to have said that, so it's probably more likely that they didn't say it often. If it was a common event, why would it bear mention in an unusual event?
Anyway, there's all sorts of things we have absolutely no idea about. It's frustrating to the serious historian, even if the problem is invisible to the casual eye. To put it in comparison: There's a "mystery" about the assassination of JFK. Some insist that the killer is not John Wilkes Booth. Yet we do know the exact time, down to the second when he died. We know the injuries he suffered, and what gun shot him. That moment in history has had tomes written about it, and so much data that it could fill a small library.
Compare that "mystery" to another historical mystery: We don't know whether King David was a real person. He's the second king of historical Israel, if real, but we just don't know if there is a person that occupied that place and time. I think that puts it into perspective: 99.9999% certainty about a precise moment versus profound ignorance about an entire lifetime
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