Append and Update issue|Power Query|Excel Forum|My Online Training Hub

I want to automate a report that displays information about our leavers during a school year - whether the students are vulnerable, Special needs etc.  Unfortunately our MIS "Hides" this information once a leaving date is entered so a simple leaving report won't work.  The data is still there but there isn't the functionality within the reporting system to get to it.  Changing the way the MIS works is not an option.

My plan was to:

Export a file dated on the first day of September to include all students on roll on that date to get all of the vulnerable data in a base table including the unique number of each student

Export a file every night with all students on roll and append to the base data table to give one "All Students" table with all information about every student who has been on roll during the academic year.

Export a file every night with all leavers since the start of the year including their unique number.

I could then merge the leavers table with the required columns from the All Students table to allow the completion of the report.

Issues that I can see but don't know how to solve:

Appending the daily student roll will keep duplicating the students, I only want to append the student if they are not already in the All Students table.

The vulnerable information does change throughout the year so I would like to update the All Students table with some of the data from the over night table.

Am I asking too much from power query?

Many thanks in advance.