Are the old books from when I got the course in August 2019 much different from the newer versions? Can I continue to use the current books for my prep?
You can continue to use your current books. The new books are a significant update in many ways - complete image replacements and a new Psychology & Sociology book. But both editions comprehensively cover the AAMC content outline and are factually accurate, so you are not working with unsuitable materials. The legacy books kept undergoing updates until their replacement in November and are supported for anyone who bought them, is still using them or simply got them with their course - as well as still being tied in to current study schedules (with the occasional hiccup!).