I wanted to examine the minimap of Deadmines, since it noticeably has some remanents of times past - I traced the areas I assumed were roads, buildings, and farms, and then looked at the eastern kingdoms minimaps for any corresponding roads. Sure enough, designer island was indeed the place where the deadmines terrain was pulled from - which also lead to an interesting discrepency between the geography of deadmines and the outside world.
As you can see in this image, I've overlayed the deadmines minimap with an inverted trace of the minimap, and layed that on top of westfall's minimap. The discrepency that I've noticed is that the doors in the deadmines would have exited to Duskwood, not Stranglethorn Vale. In fact, it would have spilled into Raven Hill.
The 'bubble' to the right is the extended land that deadmines has in its minimap, most likely denoting where water would have been, had deadmines been contained within the EK map.
This gives me a good idea as to how WestWood/Westfall/Designer Island was utilized early on during development of the game and these early dungeons.
I plan to do more analysis' projects like this, to determine where the prefab terrain came from within various instances in the game.