Quests mutual exclusion?

Is there anything in the game that prevents some quests to be present at the same time, or to be listed in a certain order? For example, I was playing around with Jared's script after I've completed his headstone quest but without ever having mentioned the search for his girlfriend. For some reason, even though I could get him to ask me to look for his girlfriend, and I could accept or refuse it in the dialog, but the quest would never show up in the quest log. The same thing happened with Appleby's sabotoge quest after I've done the Bate's guard's anti-saboteur quest; I could seemingly accept his quest, but it just would not appear in the quest log.

 

well, yeah, i know that it's impossible to legitamately complete all quests, but i was just experimenting with things. the problem i had, though, is basically that no matter how i trigger a quest in the dlg file, using qu1132 1, for example, it just wouldn't have any effect whatsoever. my guess is that there might be some other script in effect that prevents certain quests from registering at the same time or in a certain order, but i could not find anything like that.

oh, on a side note, is it possible to erase a quest or change a quest's status after it's been completed?

 

Yes, I think a quest can still be set to Botched after completion. I think that's the only state it can be changed to though.