@Switch BlaydeYou'll find some differences in grammar books, I suspect. An example would be the Oxford Comma. Some think it's fine, some don't.
There are all sorts of examples, though. The singular non-gendered use of 'they' was fine for a very long time, then 'they' (English teachers/textbook authors/etc) decided it was bad, then we as a society decided it was fine after all. The move to ban it was far more prescriptive than descriptive; prior to the shift it was in relatively common usage, but if you teach several generations consistently that something is bad, many of them will decide it's bad. I still run into people who fight tooth and nail against using 'they' as a singular gender-neutral pronoun, despite it now being commonly taught as proper and being widely in use that way.
The Holocaust example is a good one. There's no singular authority who decides what 'history' is. It's highly decentralized into textbook publishers and state boards of education and school districts and lots of other sources. This is likely a very good thing, as a singular authority over history would be exceptionally dangerous.
Yet, if a significant majority of those all decide to remove the Holocaust, we could get generations of kids who have no idea that it happened. They might even believe that anyone who claims it did is lying, because how could something so significant happen and not be 'history'?
The comparison to grammar is this: if over half the populace believes the holocaust didn't happen, is that 'correct'? That's the descriptive grammarian position. And again, I tend to go with descriptive, but am prescriptive on some things.