Saksham, according to the FAQ's of UG Admission portal, you cannot fill in different applications. You cannot register for 2 applications. You can check the FAQs here: https://ug.du.ac.in/index.php/site/faq . And the last date for registration is July 6th and if you get the NIOS marksheet in another month, it is too late by then. So for now, update the marks sheet that you have with you. And simultaneoulsy mail the helpdesk at: undergraduate2020@admissions.du.ac.in  to find out what needs to be done. DU application form has no correction window. You can make changes to your application only until you pay the application fees. But once you pay the application fees, you will not be able to make any changes to your application form. In such case, reaching out to the help desk makes sense. Because  can neither wait for one month nor can you fill up 2 different application forms. So please reach out to them.

Hello,

It is not sure if you can fill multiple applications or not. There is no official DU brochure 2020. But in 2019 DU brochure there is no such objection on filling multiple applications but it is not advisable. You have said that you don't have NIOS marksheet how can you enter your NIOS marks and upload a self-attested class 12 marksheet? You cannot give both CBSE and NIOS marks for all four subjects. The application will be available till July 4, 2020 so if you think that you can get your NIOS marksheet before the last date wait for it. If it takes more than that fill the form giving CBSE marks.