I'm not sure if there's any standards between platforms for these things that allow you to compare though. I'd say for example that you should exclude watches that last less than 5s or so. YouTube and Netflix may not have thought to do it because it doesn't make much sense to them but Facebook really needs to since I assume most of their video watches are automatic (accidental) while scrolling through the feed.
It does matter to Netflix. They don't publish their numbers and just use them for internal metrics so you can bet that they are honest with themselves about their numbers.
I'm not sure if there's any standards between platforms for these things that allow you to compare though. I'd say for example that you should exclude watches that last less than 5s or so. YouTube and Netflix may not have thought to do it because it doesn't make much sense to them but Facebook really needs to since I assume most of their video watches are automatic (accidental) while scrolling through the feed.