To the original poster: Not sure how knowledgeable you are with stats, so pardon me if I’m telling you something you already know.
The WordPress Stats plugin will NOT tell you anything that will help identify your visitors. It just simply counts how many times each page or post on your blog is visited. It doesn’t keep track of IP numbers, cookies or anything else that would help determine whether your visitors are first-timers or repeat visitors. (Or if it does, WordPress hasn’t given us access to that data yet.)
More than likely the predecessor was using a different service like Google Analytics, or as esmi indicated, they may have been using the raw server access logs to somehow determine visitor identity. (Most web servers do log the IP number of every single visitor, but most of the time, they just appear as unending streams of text and numbers unless you have software capable of translating the raw data into something more user-friendly.)
If you’re still on friendly terms with your site’s predecessor, check with that person to see if they had a Google Analytics account (or some other service), and if they’d be willing to give you the login information. If it IS Google Analytics and they setup the Analytics account as part of their personal Google account, they won’t want to share their password, obviously… so maybe you can set up a Google account for yourself and ask them to transfer ownership of the Analytics account to your Google account.
Worst case scenario: you just set up a new Google Analytics account on your own. You won’t have access to any previous stats, but at least you’ll have stats beginning from now onward. Just make sure you remove any pre-existing Google Analytics code before you insert the new code Google provides. Not sure what kinds of headaches may ensue if you have code for two different Analytics accounts running on the same site. Doubt it would cause your site to meltdown, but I don’t think you’d be getting accurate stats either.
