Hello Fatima,
regarding question 1), can you give an example? If you generate call list from within several campaign elements, then each element is processed independently and each call list is generated in a different time.
Regarding question 2), there is an answer in the same help page you have referred:
•Merging call lists
Two or more call lists can be joined together to form one call list. Use the move functions to merge call lists.
So it basically means that you can create manually new empty call list and simply drag&drop different call list into this one.
Not that one would expect under merging, right? 
Regards,
Dawood.