Firstly; There should be a way for the Devs to fix glitched quests somehow, somewhere by now. It's just been TOO LONG to have these old quests still be glitched. (and the console commands either don't work or cause FURTHER issues with the game down the line)
Secondly; If quests DO overlap (like they do), at least have the death of the NPC in question register as "quest completion" with ANY of the NPC quest givers, but ONLY upon reaching the final lines in the quest series that apply.
For example:
At level 10 you're sent off to kill "Rat A", and though you had a difficult time, "Rat A" met its doom and you revieved your reward.
The game goes on - and now you're level 34.
From a different quest line from a different NPC, you're given a quest to kill "Rat A" in order to become a member of their clan (or whatever). Even though you previously killed "Rat A" LONG ago, this particular NPC doesn't know that, and demands that this be done before you can move on. There is no convincing the quest giver NPC that you've done this already, they demand it be done before you continue with them.
You remember "Rat A" from when you were level 10, thinking that you shouldn't have a problem moving forward. You go kill "Rat A" (again) but when you get back to the quest giver NPC, they instruct you to kill "Rat A" and not to come back until you've done so. (umm, hello... I DID kill it!)
Solution: As soon as "RAT A" was killed (again), (or even having revisited the site where "Rat A" is lying dead from a previous kill) under this new quest giver NPCs instruction, a new dialog entry is then included in the responces for the quest giver NPC when you get back:
NPC - "I can't help you until you take care of "RAT A" for me"
PLAYER - "I did, "RAT A" won't bother this world again"
NPC - "Thank you for taking care of that, here is your reward."
Essentially, there needs to be either a smarter AI to the NPCs, or a built-in conversation to allow the "Hey, I completed that already" answer for the quest conversations. I don't mean something where this pops up in normal conversation, or before you actually go BACK to the quest site to kill the NPC in question (again) - that would ruin the game as whole. Just something that would activate after you've been back to the quest site under that particular quest giver NPCs instructions, and have had an interaction with the quest NPC needing to be killed (whether killing it again, or kicking/pushing/moving/whatever the dead body that remains in the world, and an on-screen notification that the quest requirements have been satisfied).
Another reason these glitches may be happening is because of the "open world - nonrailed themepark" style that the game is. Don't get me wrong, I LOVE this style for the most part. I love being able to explore and fight whatever pops up in front of me - quest or no quest. Hell, that's how I've gotten into some of the glitches... I decide to just explore and end up running through dungeons killing everything. Two days later I finally get a quest for that dungeon and everything is dead already, and the quest giver NPC is never satisfied... ARG!!
So please - if there isn't time to fix any/most of the glitched quests in the game, allow the player access to redirect the quest giver NPCs, and inform them (inform the game) that the quest they want done is in fact done.
