The other day I was reading something (which annoyingly I can't find now) that quoted the heroic JK Rowling as saying that the whole point about the Harry Potter books was that, whatever you think you know, you should be careful - because a lot of what passes for true, including commonly held 'truths', is nothing of the kind.
This brought me in mind of Hillary Mantel's epic Cromwell trilogy: I have always thought her major point is very much the same. Cromwell frequently finds the public account is not to be trusted. There's a classic, if trivial instance of this - I suspect injected into the narrative mainly to make the point in isolation - when Cromwell has to overnight somewhere as part of a mission to treat with (IIRC) the ailing Catherine of Aragon; and he sleeps with the landlady of the inn or whatever establishment he stays at. By the time he returns to Austin Friars, the very next day, a largely untrue account of this is already currency. Which makes the point fairly forcibly.
We have an example of this at home right now. For several months last year, someone I know was on a selective diet for various reasons, which caused him to make requests of hosts and hostelries etc at mealtime. It has now firmly become part of "what his friends know", that he has a gluten-intolerance. But it never was! And he wasn't avoiding gluten during the period of the diet, and never needed to avoid gluten, either - it was quite different ingredients being steered clear of. It's just that (I suppose) most people have only one way of filling out "special dietary needs", and that's gluten-intolerance. And that's with the best will in the world! No harm or thoughtlessness or anything else intended.
There must be a dozen ways in which mere mortals are systematically prone to getting the wrong end of the stick. How much of what is recorded in history is only vaguely right, or even just plain false? And how did it get that way? Obviously, sometimes it will have been the result of a purposeful effort to re-write and falsify history: George Orwell writes about that kind of thing at length. But just as often, if not more, I suspect it will be because of something far less malign.
One last example: a few years ago there was a little local project to bring to the surface a Spitfire that in WW2 crashed in a local public open space. It had attempted a forced landing and hit the deck relatively gently, upright, on the flat. And there it lay, slowly sinking beneath the grass as undisturbed things do - for 60 years! It turned out, some of the oldest local residents - when prompted - remembered all about it. Well you would ... wouldn't you?!
Aside from the frankly unexpected aspect that neither the RAF nor any enterprising scrap merchant had thought to take it away when it was still squarely on the surface** (it wasn't a war grave or anything like that - and this is the Home Counties, not the Cairngorms); it neatly illustrates how very straightforward facts, even apparently quite striking ones that you'd think would be accurately lodged, can simply slip from view. Be careful what you think you know ...
(PS: I have a little bet with myself now as to what might happen BTL ...)
** This practice (or non-practice) of leaving stuff lying where it fell was endemic for years, and not just in wartime when sheer numbers of crashed aircraft might account for it. In the 1970s I visited an active RAF station where, in a remote part of the estate (i.e. NOT the fire dump) like the skeleton of a beast in the desert lay the remains of a crashed De Haviland Vampire, left to disintegrate and sink into the grass where it had come down. It had been there for 20 years.