Hi

CBSE officials have the final say regarding this you can't probably believe internet over them. What they say is true improvement exams is for you to improve your previous scores if it's lower than your previous score then your previous score will be considered. They didn't say that once you give Improvement exams it would replace your first attempt. It doesn't work that way if you got RT it means repeat theory , you can give improvement exam again next year as a private candidate but it's your choice according to them. You can retain your old marksheet and apply for future studies using it.

Hope this helped!