A general idea on the admission process
Basic eligibility is 75% in Higher secondary.
Then next filtering is SNUCEE. People who get interview are mostly people who clear SNUCEE.
Remember, people who scored very high on JEE mains might get direct interview.
Then there are people filtered based on interview.
Probably they will prepare an internal rank list based on higher secondary + SNUCEE + interview. Remember, people who consistently perform well on all 3 will be higher up the rank. People who generally do well in boards will be expected to do generally well in SNUCEE and interview.
If people did well in all three and based on demand for a course, the seats will get filled based on preference given. Refer SSN last year TNEA cutoff to get an idea on the demand for each course.
Based on how many join from offers, seats will get filled. If people reject offers, then the next set of offers may get released for the same phase or the next phase. The process will continue until all phases and waitlist candidates are over and all seats are filled.