There is that theory too, even though I personally despise it.

This I don't agree with because Quan Chi would know that the original Sub-Zero was turned into Noob Saibot.

Your are right about that. I have actually given it some thought and I've come to this conclusion (based on pervious information given in the timeline):
Scorpion's Bio/Ending from MK1 tells us that he was given the opportunity to return and avenge his death by demons. I believe that demon was Quan Chi.
During the events of MKM-SZ, Quan Chi knew that Sub-Zero had entered the Netherrealm to take back Shinnock's Amulet. I believe it was he who resurrected Scorpion as a specter to kill Sub-Zero. It's never stated anywere (and since I had the shitty N64 version of MKM-SZ I never got to watch any of the video from the PS1 version) but that would explain his line in MK4: "To defeat my nemesis Sub-Zero I need the power of a specter."
So your point is valid that Quan Chi may have known that the original Sub-Zero was dead but there's no reason to assume that Scorpion would know that. Otherwise why would he still be chasing after Sub-Zero all the way up till MK4?

*Sigh*
Please refer to MK Mythologies for clarification on this whole, stupid, ridiculous, and done to death 100000000000000000 times topic

Hey trynax you got some time counting problems man. You don't get a baby when you're 100 years old. A generation is about 33-40 years.

I know a generation is about 40 years. You misunderstood what I said. Every Sub-Zero in the past would have had to have had a son in order for their generation to keep going. Plus: he would die sometime around 100 years because if he is mortal then his life span would only be about 100 years, and the same goes for his kinship after that. That would still give us 5 Sub-Zero's before MK1 Sub-Zero, and Sub-Zero(V) would be nearing the age of death by the time MK1 Sub-Zero(VII) entered the first tournament.

Well, Scorpion did kill him in MK1. I kind of figure Scorpion would've made it his business to know for certain.
And Scorpion wasn't chasing Sub-Zero up until MK4. After finding out it's not the same Sub-Zero, Scorpion vowed to protect him and as I said in my earlier post, Quan Chi decieved and manipulated Scorpion into believing the younger brother was involved with the massacre of Scorpion's clan and family.
Why would Quan Chi do this? For one, he said he needed Scorpion's power to defeat Sub-Zero, but more importantly, in MK3 Shao Kahn offers to let Scorpion join his army. But when Scorpion learns Sub-Zero is one of the Earth warriors he refuses and potects him. In MK4, Shinnok and Quan Chi want Scorpion as an ally and they know once he finds out Sub-Zero is one of the Earth fighters he'll protect him. So Quan Chi decieves Scorpion into believing Sub-Zero was involved with the massacre, making Scorpion break his vow.
At least that's the theory I support. Some support the theory that Scorpion never found out Sub-Zero is the younger brother.

After finding out it's not the same Sub-Zero, Scorpion vowed to protect him...
But when Scorpion learns Sub-Zero is one of the Earth warriors he refuses and potects him. In MK4, Shinnok and Quan Chi want Scorpion as an ally and they know once he finds out Sub-Zero is one of the Earth fighters he'll protect him...
This is one of biggest mis-conceptions in the history of the Mortal Kombat series. Scorpion never vowed to protect Sub-Zero's younger brother. This was part of his "What If" ending in MK2. This has been confirmed by Ed Boon and many members of the MK development team.
Besides, I for one am glad it's not canon. It doesn't fit Scorpions personality in any of the MK games. He is better off as he is rather than being someone's body guard.

This is one of biggest mis-conceptions in the history of the Mortal Kombat series. Scorpion never vowed to protect Sub-Zero's younger brother. This was part of his "What If" ending in MK2. This has been confirmed by Ed Boon and many members of the MK development team.
Besides, I for one am glad it's not canon. It doesn't fit Scorpions personality in any of the MK games. He is better off as he is rather than being someone's body guard.

People, people, people. Read the effing canon guide, as ][ombat posted. It explains everything perfectly. No ifs, ands, or buts.

See I disagree about that. I think it does fit Scorpion's character and personality and makes him and his story more interesting.
Meanwhile, having Scorpion never find out Sub-Zero's the younger brother, Scorpion becomes one-dimensional, incompetent, slow-witted, and pretty fucking stupid if you ask me.
Not to mention it completly disregards Scorpion's entire MK3 story which I think is idiotic in itself.
But regardless, that's an entirely different debate from the topic of this thread.

I've been following the story since MK1. There are 7 Sub-Zeros. I don't know about this Noob is Subbie thing, because I haven't beaten the game with either of those two characters yet. It could be a what-if ending.
As for MK:C, that show could be somewhat canon. The Scorpion in MK:C is Takeda, not Hanzo Hashashi.