Board Thread:The Three Doors/@comment-4977079-20150725060208/@comment-29517617-20160607105054

Perhaps they are counted as one. Remember, the Shadow Lord's influence on the land didn't actually end before the end of DQ3. He still had the Four Sisters set in place, poisoning the land, and making people sick as well as hindering crops from growing. There were probably also still spies in Deltora, and his crystal was still in the palace as well, and he used that to torture Lief. Going by this, in a way, at least in spirit and mind, he was not gone or repelled at all. He was physically driven out himself, but all of his power was not.

It could also take place just before, slightly after or during his third defeat in DQ3. If it was shortly after, news of his defeat would spread slowly at first, and people on the other islands might not have heard about it yet. This makes some sense to me, since The Three Doors was the second story we got after DQ3, so there's no books taking in-between which can disputed the theory.