The answer is Yes and YES. :)
We attempt to maintain a global tree, which means that we only want 1 profile per person on the site if at all possible. So when you encounter another profile that matches the person you want to enter, go ahead and connect to it. Once you've done so, please proceed with improving that other profile if you have additional information to add. There's a box (between the fields and bio section) where you can add the reasons for your updates - I'd recommend putting in a brief line about what you're updating and why there. Keep in mind that we're also a collaborative group, so we all try to help each other out. I'm thrilled when someone edits one of my profiles and am never more excited that to dig in and find out what they put there and why.