Wow, lovely ageism there! You should actually be fucking ashamed.
I mentioned "millennial arrogance" meaning the arrogance was millennial: internet communication now means mutually affirming discussion on your sub-reddit of choice is often seen as just as valid and worthy of respect as proper research or study. It affects all ages, sadly.
The term Mandela Effect is offensive, as was described above, and coined by a paranormal investigator after meeting other people, who, like her, believed the Nelson Mandela had died decades before he did, and so ascribed some sort of "woo" to this.
Imagine being so titanically ignorant and ill-informed as to have thought this? Mandela's 1990 release was worldwide news, and his subsequent election as leader of SA was monumental for various reasons and made him the most internationally famous leader at the time. He won the Nobel peace prize, and met the queen, Bill Clinton, FFS. Why would you want to associate with this Olympic level stupidity?
I don't know how to break this to you but sometimes words invented post-1973 can be ... useful? For describing distinct social and cultural phenomena?
Yeah, I was born after that actually... and mistakes and/or false memories are NOT 'social and cultural phenomena'. They've been around as long as people have, and have been much studied by psychologists, psychiatrists, scientists, criminologists.