A different "expanding the map" question:
When the rules say 'each continent tile must be placed adjacent to another already placed continent tile', does the word "adjacent" include placement wherein my newly placed continent tile abuts a previously-placed tile along an edge, but there is another segment of that same edge of the newly-placed tile that does NOT abut a previously placed tiled?
I'm not sure I've totally understood your question (sorry for my english). :-)
However, when you place a continent tile:
- all the boundaries' constraints between tiles (land with land, sea with sea) must be fullfilled (no constraints about the pre-printed island on the map);
- at least one segment must be adjacent to already placed tiles.