How do I version a proofed website

I have looked all over and I found a fair bit of information on how to create a proof of a website, but what I can't seem to find is how do I go about versioning that same proof. I know for non-web files (PDFs, PSDs, Tif files, etc.) when you click on the Version dropdown, there is the option to add a new version. But when I look at a website through the Workfront Proof Viewer utility, I don't have the option to add a new proof. Even as the global admin, I can't seem to do anything other than comment on the website proof. I figure someone here will know something that I overlooked, because I am stumped.

Thank you!