What Lindley said. It will give you the total file number, but it's only copying the ones that aren't in the destination folder when it checks. It doesn't know that until it gets to them so it gives the total.
It said 30,000 files to copy, 143GB, 5 hours remaining.
I know what I saw. As 12,000 files were already in there it shouldn't have said what it said.
Sure it should. It sees 30000 files in the starting folder, it needs to process all of those. As it progresses it may figure out that some of them don't actually need to be copied, but it doesn't know that up front. (It could check the destination first, but for efficiency reasons it doesn't.) This is exactly what Guartho just said.
As for the estimated time remaining, I think we all know that can be wildly inaccurate sometimes. Although lately it seems like they've been doing a better job at estimating that.
But in Windows it wouldn't do this. It would automatically skip over those in there.
In the Mac the progress bar started from scratch and started counting down from 30,000, IE I'm starting again.