I cannot definitively say whether Tezpur University and NEHU accept class 12 betterment marksheets for CUET UG counselling without referring to their official guidelines.

The CUET UG information brochure or website might mention the validity of improvement marks. Both Tezpur University and NEHU likely have specific pages dedicated to CUET UG admissions on their official websites. These pages should mention accepted documents, including marksheets.

If the information isn't available online, you can directly contact the admissions department of Tezpur University and NEHU for clarification. They can provide the most up-to-date details on their policy regarding improvement marksheets for CUET UG counselling.

https://university.careers360.com/download/ebooks/all-about-cuet

I hope it helps!