I'm having a tough time following your question so let me just explain what I think you're asking.
Although you can convert an sRGB image to Adobe RGB, the gamut is still no larger than the sRGB gamut.
For example if you convert from Adobe RGB to sRGB, you throw away all that extra information, converting it back to Adobe RGB doesn't restore it, it's gone forever.
Proofing is used to "simulate" the output.
If you chose to simulate sRGB and can use Cmd+Y to toggle that view off and on to see the difference.
You may not see any difference depending on the image.
Normally Proofing is used to simulate a printed output.
If you're printing to a desktop computer you choose the profile of the exact paper you're going to use.
If you're image will be printed to a commercial printer you choose the appropriate CYMK profile.
Is Proofing accurate?
Previewing your Adobe RGB image using sRGB is probably accurate, for your monitor.
Previewing a print output isn't very accurate but it can still be helpful.
