I almost ran into this issue myself. I purchased a MacBook Pro in 2012, but didn't buy AppleCare at the same time. Later in the year (Apple allows you to purcha

I almost ran into this issue myself. I purchased a MacBook Pro in 2012, but didn't buy AppleCare at the same time. Later in the year (Apple allows you to purchase AppleCare up to one year after your hardware purchase), I decided to buy AppleCare in order to extend my warranty from one year to three years. I bought AppleCare from Apple's own online store, but didn't realise I had to additionally register it. By chance, I had a Genius appointment at one of their stores a few months later. When I mentioned I had AppleCare, they gave me a blank look and said it wasn't on their system. They asked if I'd gone to the website to enter the serial number (which I hadn't), so I did it when I got home with a few days to spare. It was my mistake (technically), but I wasn't impressed.