When do game-changing spoilers stop being treated as spoilers?

[2Quick]

When does a spoiler in a video game start to be o.k. to talk about?  

 

Some spoilers, like Sheik's secret Identity in Ocarina of TIme, or the final boss of Twilight Princess, or Liquid Snake's parentage, are common knowledge, and not taboo to talk about.   However, I believe everyone's enjoyment of the game would increase if it was a suprise.  When does it become O.K. to openly discuss different spoilers?  is it a set of time?  or the way the developers handle it?  I'm curious while some spoilers( i.e. Rockstar game endings, The Walking Dead, Journey) are still handled sacredly even though a bunch of time has passed since their release as well.