as Suzaku says... it should be based on world alone.

If character progression affected worlds we'd know about it by now. Its very easy/tempting to visit new worlds, be it own, friends or whoever else, in an end-game character that had everyting completed. Or So chances that we'd learn about this now are near-zero.

What could happen is that somebody trolled and killed the boss, an admin could have messed something up, or its a game bug.


edit: wait, draugs? ... with elder dead? ... i think there are two mechanics here... one is random creatures spawing (and/or one type of invasion) being unlocked after relevent boss is killed. But there is another type of invasion that the yet to be killed boss sends his minions for an attack. (i think this is weaker invasion)... so most likely thats what happened.