Rime In The Original Myst 
I thought this was very obvious for a very long time... but apparently I need a "source" to keep something completely obvious in the article. 

In the original version of Myst, there is a Topography Test that you can punch in at the Forechamber Image Generator. A little holograph image of an unnamed island covered in snow pops up and rotates for a little bit. I believe the code was "40". It wasn't of any known existing Age at the time. Anyway, when realMyst came out with the added "Rime" Age, you began your journey to access that added Age by punching in the same code you would in the original Myst for the Topography Test. Point is: the same image pops up that did ever since 1993 and the first edition of the game: a snowy, mountainous looking island that is unmistakably Rime itself, now with a name and playable aspect. Thus, it's painfully obvious the designers developed this new Rime Age based off the unassuming novelty holograph from the very first game. 

Yet I'm being challenged on this for not having a "source".  ...  -_-  .... wow. Well, can't find a perfect little source for you, nor did I think this necessitated one. Thus, if anybody can get a definitive "source" for the desperately contradictory Wikipedia regulars around here, please add it to my edit regarding Rime. Jeez. Thanks, - AL.  74.56.51.128