Dear Aspirant

The concept of Improvement exam is simple, if you score more than your previous year's marks, then your marks will be changed with the new ones. For Example You scored 85 in Physics in 2020 and after giving improvement exam in 2021 you scored 93 then 93 will be your new Physics marks.

You will need the old marksheet only if you score less than the previous year's marks in some subjects, because then previous marks will be considered. If you give improvement in all 5 exams and score better in all 5 subjects, then your improvement exam marksheet will work fine, but if you improve in some subjects and score less than previous year in some, you would have to carry/upload  both of your marksheets everywhere.

Hope this helps