Usually an alternate list implies that they have extended (or plan to extend) all their spots. Then they rank everyone else, and as the "no thank yous" come in, they start offering positions to those on the alternate list. For the most part, numerous people get spots off an alternate list (like 20+, or I've even heard 40+ at some schools). Did they give you a specific number (ie You're 16th on the alternate list)? If you're in the top 20, I'd say you're golden. If you're lower than that, it just depends on the school. You could call and ask. I would think they would be very up front about this.