The Slim Shady LP was the first time I heard something in advance because it leaked to the internet. Something like 6 months before the release, my buddy who went to school up north excitedly told me about him over the phone. The scene up there was already buzzing over the leak. I didn't have a computer yet, but that Thanksgiving when he came home, he broke me off a tape. It was still a month or two until the release date.
It turns out that I already had seen him on home video of the Scribble Jam battles that my graf-head friends shot, but the video was so blurry, I didn't realize it was the same guy until later. He lost that battle, though. I don't think he even made it to the final round. He seemed really off his game, like tired but presumably he was also super fucked-up, knowing him.
After seeing this post and video, I now know this is wrong, but the way I heard it was that Dre first heard Em battling on LA's Wake Up Show with Sway and Tech. Em did battle someone on that show (maybe it was Juice?) because I used to have a tape of that, too, but I guess he was just doing that on the side while he was out there. He officially lost that battle, but not to me; his freestyles were soooooo ill.