Okay, I'm a few cycles removed from the application process, but this might help some of you make sense of the status messages. Forgive me if there are some in-between statuses that I'm forgetting. It's been a while.
Pre-interview message "Letter will be mailed" = rejection
Pre-interview message "Re-review later" = hold
Once you've had your interview, you will get a few different status messages:
Thank you for scheduling your interview -> Under review by a member of the ADCOM -> Under review by the committee -> Decision reached, letter mailed
This can culminate in a rejection, acceptance or waitlist.
"Under review by a member of the ADCOM" means a single person is looking over your application and they will present it to the committee later.
"Under review by the committee" means that your application has reached the committee room and they'll look over and vote on it.