I agree. I haven't deleted any of my swords but I obtained all three before trying to get any of the exotic swords. I then upgraded two swords to 280 light on the same character and now I can't get the Dark-drinker. We did all three knights at the same time because my two fireteam members were going for different swords than I was (It was stupid hard btw, I don't recommend trying it that way. Just do one or two at a time unless you're well over 300 light). I've tried switching the sword back and forth and the exotic quest never pops up. I assume raising it to 280 light is the quest trigger and maybe it would've worked if I hadn't already started the arc quest on my titan when I did it. Deleting a character and starting all over sounds incredibly painful. Even if I can just straight to level 25, getting all my classes upgraded would take forever. I still haven't finished nightstalker.