I know the general consensus is that the N64 build was never truly developed beyond the train, but I suspect more work was done to at least the training facility portion of the game than anyone would be lead to believe.
I spent a long time hacking the Biohazard 0 Trial Edition on Gamecube, and recently got back into it. That demo is also not terribly "developed" beyond the train, but all of the areas are present on the disc (just takes a little hacking), at least in some early/semi-playable form... and some look completely different from the retail game.
What a lot of people don't seem to realize, is that this demo is basically a full prototype of Resident Evil 0. Sure, it may not be the N64 version... but it's pretty much the middle ground between that version, and the final Gamecube release. Hell, it even has a fully rendered cutscene from the N64 build on the disc. I didn't personally discover that one, but the fact that it's on there is mind-blowing. Rebecca is also still voiced by her N64 actor in the demo.