You can checksum them, might be faster than delete and retransfer. Some tools can do that for you at scale; I forget if rsync that that ability or not. Not sure what os or tools you have available, though, so ymmv.
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should I delete in New Hard Drive and re-transfer?
Sometimes this makes sense to do, but usually it's not ideal. Doesn't sound like deletion and copying again is the right choice for your situation IMO.
With a program like FreeFileSync you could simply compare the two directories and have it highlight any differences. If one file is missing it'll show you and let you sync the directories. If you're concerned about data integrity on the copied destination there is a content comparison mode that will verify both sides have identical bit perfect files or highlight any that have differences. There are other programs and tools to accomplish the same but FreeFileSync has an easy to use interface.
Thanks, I'm using "Beyond Compare" and that apparently does the same-ish thing but I'll take a look at that. I'm guessing that I must be mistaken in my mind; it seems like both file sizes are the same and that the same number of folders and files are in both hard drives. So I must be remembering something incorrectly. Thank you!