Official comment
Hi Denny -
Actually, we do track contacts via cookies prior to them opting in, so the tracking information may indeed show they visited those pages. A global Rule can then tag them based on the landing page visit. I'll update our ticket so our first level Support people are aware of this advanced feature.
Here's an example made in your account. I visited a landing page at 6:50 AM PST, and then filled out a simple opt-in form I created at 6:56 AM PST. In the Automation Log below that you can see that the "New Contact" was created at 6:57, after that form fillout. But the landing page visit tracking showed up before the contact was created at 6:50.
Tracking information is delayed in the Contacts database, so it may take up to 15 minutes for the page visit to show up after opting in. A global Rule can trigger on the landing page visit and add a tag; an example is shown here.

The disadvantage of this is that some people have cookies blocked, so the landing page visit would not show up. Our experience is that this is rare.