You are absolutly right, it appreas that more and more gankers are not on zkill anymore.
https://forums.eveonline.com/t/nerf-ganking-megathread/299004/588
But there is an easy solution to that, add your corp / character to zkill OR post your losses against gankers by hand.
My code handles manual added or delayed killmails separately, to prevent false positive or false negative detections.