Acheivements not blocked after using cheats

I have GTA: IV for the Xbox 360 and even though i have used cheats i have been able to unlock achievements. when i use a cheat it will still say that a certain acheviement has been blocked but then i have unlocked that achievement afterwards. For example, i would put in the health cheat and it would say Cleaned the Mean Streeets was blocked. I then unlocked the achievement and now when i use the health cheat it says Finish him is blocked. I don't know if this has anything to do with this but i bought and played Episodes from liberty city before i bought and played GTA: IV