By the way, if you have any question about data integrity on any system, you can create an MD5 checksum of the source and target files. On Mac OS, you use the ‘md5’ command.
dtm$ md5 dorymonster_test1.mp4
MD5 (dorymonster_test1.mp4) = f3ed1559874599d26fddc5802d65266e
Do that before and after copying them, and you compare that the result is still the same. In the example of my particular file, it’s “f3ed1559874599d26fddc5802d65266e”. There are free MD5 apps on Windows or on any other OS, and I don’t know the names but they’re the same algorithm with the same results.