Erasure is different than censorship, and I think you're intelligent enough to know that. I took that AP history class, and it was super biased against the workers, so that's kind of a joke to reference.

Also, if we're talking about a country with a seventh grade average reading level, we're mostly talking about people who have never taken an AP fucking US history class.

Choosing the September date is part and parcel to why more people don't know about it, because it's not generally part of the public consciousness or conversation. That's called erasure, not censorship.

More that the US has successfully managed to censor entire swaths of history by limiting education (especially in red states) and ensuring that critical thought is not taught or enforced in any meaningful capacity. This is all totally intentional and verifiable. The information is there, but people are literally not ever taught (in academia) to think critically and seek answers to things they are unsure of. It's mostly just memorization until you get the churned to the next year of memorization and if you do dare question any of it you get shit on by peers and teachers alike for being a know it all. It's rare that you find people willing to foster curiosity in children which ultimately blooms into people eating up whatever they're told as truth.