Still a wee confused but I think I’m closer to seeing what you are after. At least by the use of the Option Click History step part. I’d think you would want to compare your soft proofing adjustments to the photo as it was originally edited prior to the initial soft proof editing. I think the fundamental disconnect here is what we end up with and see asking for Before. As you state, when you ask for this, you get the image as it appeared from import, you lose any subsequent edits you applied up to this point prior going into Soft Proof right? That is a problem. And a Snapshot doesn’t appear to help us here.
Sigh, it looks like I somehow didn't hit "Post" to my answer to this a few hours ago.
We are on the same page.
"Before" has to be the end of working your master, before you start making output specific adjustments. And also we are in agreement that it is much better to make output specific adjustments on the proof copy, not the original. In my post I was just providing viewing comparison options for both scenarios.
To make clear, in the (less optimal) case of making output edits to the master, here is what I mean to get Before and After to work as needed:
1. Import (History step 1), adjust highlights (H2), add saturation (H3). Looks fabulous = "Master".
2. Turn on soft proofing and set profile. Loses contrast, so I want to add some.
3. Increase contrast (=H4). Dialog pops up, I select "Make this a proof."
4. Turn on Before/After (Y)
5. In History, right-click on H3, and copy history settings to before.
Now Before is the "Master", and I can adjust "After" to try to match it.