All my VC's soft proof as the VC's color appearance. Not the master. Then while in Develop, Soft proof, I make an edit, that itself creates a proof copy.
Andrew, being unsure just what you are saying here, I performed the following experiment:
1. Chose a previously unedited raw image
2. created a VC from it and made a number of gross edits, so that it was clearly different from the master copy
3. created a VC from the image in step 2, changed the color mode to B&W, again, clearly different from both the master and copy 1.
4. entered softproof mode on copy 2 and created a proof copy
5. selected the Before/After Left/Right display. The right image was the proof copy, the left image was the master image, the unedited image, rather than copy 2.
This was done on a Windows 7 system, perhaps the Mac versions work differently or perhaps I really don't understand what you've said.
Alan