Questions on Profile Searches, Exclusions, and Merging Lists

I initially ran a search for 1,000 profiles. Then, I ran a second search while excluding the first list of names, but it only returned 611 new profiles. Given my filtering criteria, there should be more than 2,000 profiles available, so I expected a higher total. Could you explain why this happened?

I also noticed that despite excluding the first search when running the second one, there are still some duplicates between the two lists. Why is that?

After merging two lists, is there a way to exclude the entire merged list from a new search? When I attempted this, it only excluded the original list, not the whole merged one. If possible, I’d love clarification on how to properly exclude merged lists.