I interviewed in early March. I had a decent conversation with Mary Brown about their admissions process. She said that most applicants will be placed on the waitlist until they are done interviewing. If you do not get a rejection within about 3 weeks, they have waitlisted you. They do not rank the waitlist. I was a little puzzled by this, so I asked her how they fill the class. She told me they attempt to fill the class will students that will provide a certain atmosphere of quality that Dartmouth wants. I got the impression that they want a certain dynamic, and not just high scores. What this means is that once they sent out acceptance, and people decline, the admissions committee looks for someone from the waitlist that will fill that spot.
I hope this sheds some light .