I would think inaccurate GPS data is likely to be an issue as well. Read an article about how Australia is out by over 1.5 metres due to the tectonic plate it resides on moving about quite a lot.

I’d say old GPS data could also be an issue. Just recently I read that all GPS data for Australia is completely out by over 1.5 metres. Due to the fact Australia resides on the most dynamic tectonic plate in the world. I’d say that’s likely to be a large factor as well.