Quote Originally Posted by Shattered Dreamer View Post
A retcon does not count as a plot twist.
In its actual meaning, a retcon is, by definition, a plot twist occuring amongst different stories.

Retcon

For Meryl & Otacon to be in MGS4 neither of the endings in MGS1 can be what really happened
(SPOILER)Otacon doesn't die in the Meryl ending, technically Meryl doesn't in Otacon's either, it's only assumed that she's dead. During the optional flashback in MGS4, I believe the last shot you see of her is her lying in a pool of blood after the Sniper Wolf incident, so i think the game might imply that either ending could have worked.