Option A is the correct approach as it involves performing data validation checks on the data before and after the migration to ensure data completeness, consistency, accuracy, and integrity. This helps in identifying and addressing any issues with data quality during the migration process. Option B is not reliable as the data in the old system may have inaccuracies or incompleteness. Option C is a good first step but should be followed by data validation checks. Option D is incorrect as data quality is critical for the success of the migration project.