Defining the Mandela Effect isn't really easy, the official creator, Fiona Broome has her own definition:
My research began in 2005, after someone in Dragon*Con's "green room"
mentioned that others (besides me) remembered Nelson Mandela dying in
prison. A lengthy conversation followed. For hours, a group of us --
mostly authors -- discussed our own memories of that event, as well as
other events that don't match the timestream we're in now.
That's not a conspiracy theory. It's related to alternate history and parallel realities.
Well, I was convinced at "Dragon*Con's 'green room'," but I have to admit, she's absolutely right; that's not a conspiracy theory, but rather a self-reinforced delusion teamed with denial of just how terrible one's memory can be, she goes on:
Exploring the quantum / "Sliders" concept further, I discovered an entire world of shifting realities that people try to reconcile daily.
Sliders concept? Sounds delicious...
Oh of course, a 90s TV show:
I was, and still am, a fan of Sliders, I even watched the pilot when first aired -- shows you how with it I am. Yes, I even own it on DVD in that shitty case which tries to scratch your DVDs and ruin them.
The Sliders analogy is seemingly downplayed now that the Mandela Effect got some more mainstream attention, and instead Fiona tries to be a bit more light about it sometimes, suggesting that it could be glimpses into parallel worlds, however for the most part the true believers make it sound more akin to literal memories from alternative realities and even sometimes directly take things from the Sliders TV show. In other words, when they remember something incorrectly, it's not because human memory is terrible, but rather because reality itself has been changed à la The Matrix.