This will be half a rant, half my experience with research - and the way confirmation bias can lead to missing information.
I visited the village of Austerlitz a few months ago, now called Slavkov u Brna in the Czech republic. An international Napoleonic research fund maintains a cozy museum dedicated to the battle of Austerlitz, and there is of course a beautiful memorial seated right close by - at the Pratzen heights, where the coalition's leadership formed their ranks and where they made one of the biggest blunders in military history, costing them over 30,000 soldiers slain or captured, and eventually the whole war.
My fascination looking down from the hill wasn't only with the beautiful and vivid Czech villages that sprung up and developed in the area, but with the sheer scale of the battle. I have read dozens of descriptions and accounts of the battle, and even as the landscape changed clues of the old age were there: the distant estate in Sokolnitz with its (largely abandoned) gardens, the buildings of Brünn (Brno) on the horizon - I couldn't see the fabled Satschan pond as it had since been devoured by irrigation and the many corn fields its waters likely fed.
There was a scale to it; a scale I couldn't understand or feel right when reading those accounts or when glaring at maps.
The importance of the landmarks mentioned bore a special historical interest to me; it was Sokolnitz where Marshal Davout's III. Corps deployed during the battle and managed to push the coalition forces back, eventually into the fabled lake - reputedly its ice broke under the weight of French shelling, hundreds of soldiers drowning in its icy waters.
The heroism of the Marshal's Corps is one of those historical details often glazed over, for good reason: it's a detail that completely undermines popular / orthodox perception of early modern warfare with a conundrum researched in-depth by scholars to this day. The III. Corps was ordered to force march from Vienna to Austerlitz and join the battle. They did so in under 48 hours, deploying soon after - and while doing so, they covered a whopping 120km (75 miles) on foot, a feat seldom replicated in history as it's a far stretch even for modern infantry - the infamous Falklands march of the Royal Marines took a heavy toll on them despite being 2/3 a length, and despite them having one additional day to cover the distance.
Seldom replicated, except for the exact same time period - over, over and over again. In the autumn of 1806, Prussia caught Napoelon by surprise with a war declaration and an invasion launched. Opting to go on the assault, the French gathered what troops they had available in the theater for a counter attack and 19 days after the war declaration they entered Berlin, triumphant. Such velocity of action has been wholly unheard of and still baffles me; a campaign covering a larger distance than Germany's 1939 invasion of Poland, much faster and without machinery, motorization and airplanes - with soldiers on foot & horse. Similar feats achieved by the British troops in Spain, by Russian troops in 1813, by the French in Italy, by Austrians in 1809...
Far from a coincidence or isolated examples, but again - glazed over. I have read dozens of "worldbuilding resource" articles that dealt with advice on writing troop movements and armies. They each had one nefarious detail in common:
The missing Napoleon.
Why, though? Is it ignorance / lack of knowledge about the period? Or it might be easier to simply glaze over the Napoleonic wars / early modern warfare when writing these articles, as otherwise the author would have to insert a whole chapter on explaining why Napoleon's time had things different. This in turn has led to a whole in most of these articles. I ended up with a rule-of-thumb: whenever I open something of the like, I search the page for some quick references and if there's a Missing Napoleon, I take it with a grain of salt. You'd be surprised how many there are.
Wouldn't it benefit an article detailing troop movements or armies to dedicate at least some word to armies marching without a supply train? To cascaded movements? To discuss amphibious warfare and its roots? To detail rocketry, early terror bombing, ambulances, military organization, etc.?
The phenomenon is not unique to Boney; I have been trying to keep an eye out for specific details of the kind; topics within greater research that are contradictory to the mainstream /but/ are very much relevant and often glazed over. So sorry, no non-eucledian Geometry here. There's many, but they're hard to find - specifically due to the Missing Napoleon - how do you catalogue and learn about something that is baseline omitted from articles for being contradictory?
There's of course articles that specifically say "Hey, this is usually glazed over, but HERE" - I enjoy those, a lot to learn about Victorian times - tattoos, mannerisms, extreme sports, etc. It's how I originally learned that the Regent of Hungary, Miklós Horthy, had a gigantic golden-green dragon tattoo decorating his body. Then there's of course the fabled discussion on "Ramming", the practice of driving one military vehicle into another. Hot topic for tanks, interesting for airplanes and completely historical & plausible for ships, even in examples such as the USA's Civil War. Often we perceive "ramming" reserved to ancient warfare's triremes.
Napoleon hits close to heart because it's a favourite topic of mine, but also a period of history in which I'm immersed to a degree that permits me to shoot "Actually"s in discussions over politics and military. And that's pretty much how I learned of the Missing Napoleon.
Do you know any other topics of the kind? Where the mainstream is contradicted by a specific time period, a specific country or set of events - to the point people rather glaze over it than expand into a deeper explanation?