You'll probably have to use the function to upload your world to the world viewer to get an accurate layout. If your world is old and goes through the updates it scrambles ♥♥♥♥ in a unique way and wont be the same as fresh world of the same seed.

My buddy and I had this issue literally last night. My assumption is that when mistlands was released it changed our worlds, which altered anything we hadn't uncovered yet. The seed generator showed exactly where everything was, like you said, and everything we found matched up except yagluth whom was next. We ended up having two places for yagluth, and one wasn't there. The second one was. So I'd see about finding a different one if possible. If there isn't then I'd contact the devs about it. Trying to sail around forever, checking every plains isn't fun.