This is a rather minor non-issue, but I've been wondering how widespread it is. I have a 2013 11-inch MBA and ever since installing Yosemite (as far as I remember), the Mac model info in the About This Mac window (e.g. 11-inch, Mid 2013) is missing. It only says MacBook Air, nothing else (even after clicking it), see the attached screenshot. I also have an iMac and it shows its model specifics properly. Of course, I do know what computer I have, I'm just wondering if it's a bug I'm having on my specific machine or it is more common.