Please confirm if my understanding is correct about your requirement -
1. You receive a QVD file having 24 Months data, and you're generating 24 CSV files for each month.
2. Now, you receive a QVD file again having 25 Months data (24 Months Old data and 1 Month new data). Since you already have generated CSV files for 24 Months Old data earlier, now you just want to generate one file for the 1 Month new data.
So, to summaries your requirement - it should generate CSV files only for the new month data? Is that right?
If yes, can you please provide some of your samples data, better yet the script you are using. It will help us to find the solution.