hello dear,

In UPSEE 2020 document verification you have to submit the valid documents. In your case if you have 2 marksheet including one of improvement then you need to upload it both. While registrataion time you will need to provide the exact details for the 12th board and it is given on the registration page where you need to upload the both the marksheet. There will be no issue in attaching both the marksheet.

all the best!!