This is specific info from AAMC:
1) they will have to re-enter ALL the AMCAS data or can they still roll-over info from last year? Re-applicants to the 2004 entering class who submitted an application to the 2003 entering class will not need to re-enter their application data. Applicants to the 2002 entering class, as well as students who created but did not submit applications to the 2003 entering class, will need to re-enter their data.
2) there will definitely be no confusion about a registration they submitted last year from one this year? Certain of these previous applicants (a small number) will need to re-register with the AAMC. Confusion should only occur if 1) the applicant entered incorrect (made up) biographic information when registering in a prior year, or 2) the applicant elects to enter incorrect data when during AMCAS 2004 registration.
Most applicants who have previously used an AAMC application, such as AMCAS, FAP or the MCAT Additional Score Report (not including MCAT Registration, which is hosted and maintained separately), will be prompted to change their password. This indicates that the system recognizes the applicant, but that the applicant must change their password prior to beginning the application; during this process the applicant will also be prompted to select a security question (such as "What is my pet's name") and provide a security answer ("Spot").
3) that our documents that had last year's AAMC ID number for them should be changed to this year's new number, or will they be assigned the same number? An applicant's AAMC ID should not change from year to year. If an applicant is issued a different AAMC ID, that applicant should contact AMCAS with both AAMC IDs. That said, in certain circumstances, we must change an AAMC ID (usually to address inaccurate registration information entered by the applicant, as mentioned above). In these rare instances, we are changing the ID to ensure that 1) all applications associated with the same individual are linked the same AAMC ID, and 2) MCAT scores are associated correctly with the individual to whom they belong.
Applicants should contact AMCAS if they 1) discover that they've been assigned a new, different ID, 2) find that their prior MCAT scores are not associated with their AMCAS application, or 3) submitted (not simply completed without submitting) an AMCAS application to the 2003 entering class and are asked to re-enter all application information.