* No central tracking: There isn't a single organization that tracks every sale of every book, especially over such a long period.
* Different editions: The book has been reprinted countless times, in numerous formats (paperback, hardcover, ebook, audiobook, etc.) across different publishers.
* Historical sales: Sales figures from the 19th century and earlier are often incomplete or lost entirely.
However, Pride and Prejudice is considered one of the best-selling novels of all time. It's been continuously in print for almost two centuries and has been adapted countless times for film, television, and theater. It's safe to say the number of copies sold is astronomically high.