Where did you hear this??? What would be the reason for this small number being accepted early? I thought Duke had a strict release date in the spring for all acceptance letters.
i was notified about 3-4 weeks after i interviewed, so mid/late-november, with letter etc...
a lot of schools who have 'fixed non-rolling' dates for both med and mstp do tell some candidates early. a few, like baylor and duke actually send letters/official word - though others like yale/columbia/one other place i can't remember (my experience) will let you know through unofficial email, phone, or on the spot (i won't say which method for each of the schools). i'm not sure of the frequency of this occuring, but my sense is that it is exceedingly infrequent.
this is different from a school saying that you have a 'very good chance' or 'will probably get in' or 'i'm sure i'll see you in the fall', which while are encouraging, don't necessarily convert to acceptances. also, some schools give no indication, but also result in outright acceptances.
don't be disenchanted by hearing that some schools do this, or worry that you will be at a disadvantage if you interview later - many of the 'early-notified' people aren't high-yield matriculants (other offers etc...), and as i said before, the majority of _matriculants_ are those who have been accepted either on the date the program sites, or off a waitlist.