Hi

Improvement exams are an opportunity given to candidates to improve their previous scores. If the scores they got in the improvement exam is low than their previous scores then it's not considered. Your previous scores or original marksheet will be valid after that. RT stands for repeat theory meaning you didn't get the minimum marks needed and since it's an improvement exam it's not mandatory to appear again or to be precise it's your choice if you want to appear for the papers again or not. CBSE doesn't have any say on this the decision lies with you.

In short your previous scores are valid.

Hope this clarifies!