Currently Online 
How do you want to measure it? I mean, I guess you would just check Gamepass numbers from the CoD release month and compare it with the month before but that would be illogical.
Many don't just subscribe for a single game. They subscribe because they know they will get constant releases of games like that. And there will be people who have subscribed already months ago because they knew games like CoD will release. There will be people subscribing in a year knowing there will be X different CoD games and most important, a part of every new subscriber will pay for years.
I don't pay for Gamepass because there is Halo or Forza or whatever on it. I pay for it because there are Halo and Forza on it (and the other games obviously)
And not to forget, more players means more people paying for in-game currency and stuff like that. That's the whole reason why Fortnite prints so much money. CoD had more players than ever which probably means it also has more people paying for skins or the next DLC.
