Does anyone know?
Most likely not. You’ll probably have to restart the whole process again. They have to restart the whole system and delete the usernames of the older applicants because you never know when someone will have a similar name configuration.
Not exactly sure what you mean by ‘Student ID’ but I do believe that they either add on to the same file or at least have a (metaphorical) link to your previous application… In my MX interview the AO clearly stated that she was looked over my application from last year and made some comments about it… For Milton, when I called about something related to this year’s app, when they searched up my name, the lady on the phone asked “if I was the same insert name from last year and if I was a re-applicant”. Similar thing happened with Exeter… And those were the three school I re-applied to this year… So I imagine that while the AO’s make an effort to look of re-applications with fresh eyes, I suspect that they treat past applications like a supplementary item.
I’m pretty sure that Hotchkiss uses the same id to track all contacts/applications/etc. My son went to their portals program and they used the same id for his application to 9th grade.