Originally Posted by GGN Sumidor
That's where you're wrong. It does matter. You cannot use cheats at all in an act, or it will disable the achievements entirely. You have to complete Act 9, in its entirety (kill the Immortal and everything) before it will unlock.
Ah fack. Well I took it back thinking it was glitched and I didn't feel like bothering with it, well looks like I'll get it again.