When you send your GMAT score for an exam taken at a test center, the school will receive the scores from the exam you sent and any previous test center exams. If you retake the GMAT exam after sending your scores, your new scores will not be sent to previously selected schools.
When you send your GMAT score for an exam taken online, the school will only receive the score for the appointment you selected to send. If you retake the GMAT exam, the schools you selected will not receive the new score unless you choose to send it.