why dont you try removing the new guys from the bottom of the new list. Then merge the new and old lists and get the number of duplicates.
(original list - new guys) - duplicates = number of guys that have left.
In any case the total number reflects the net gain which is whats important.
The result will also give a list of guys by name that have left.
Would love to know how many staff they have locked in some dark room in the basement who do all of the manual insertions and other manipulations....Hopefully Dr Muller will sniff them out when he comes.