very interesting subject @kona and very interesting discussion.
I agree with you in that I dont think the Mandela effect is true. our memories are unreliable, but sometimes they also come from our perception of things.
our brains are full of details from our daily lives. These details attack our brains every milli-sec whether we like it or not. and for us to remember everything correctly, our poor brains need to sift through all the garbage to collect relative materials.
Its no wonder that we tend to mix things up. especially things that were imprinted in our brains through strong emotions with facts. Like the Mandela example.
Probably when he was imprisoned, people were thinking that he would have been killed, etc. The emotions attached to the events at the time were much stronger than the emotion attached to his release and normal death.
Our brains mainly work to preserve more of the images we feel strongly about for long term recollection. In this case Mandela dying in unfair trial for a cause which makes him a hero. The hero we all want to be vs Mandela getting out of jail and dying a normal death and nothing heroic about that for us, its just being like everyone else.
And now... Bingo! You get a lot of people believing the hero story, even when they don't know each other. After all, we all have more or less the same brain biology/psychology imprint.

Thanks again for sharing. I am glad I read it before the vote deadline :D