I clarified it and it seems we could use the eVar Instances as a counter as well. Though we keep the extra event and leave it as a normal counter.
But still I don't see why it doesn't work with a value. I've seen in the documentation that you need H23 Code, that this works. Where can I see what we are using, maybe this is why it isn't working.
I now also added another event to the milestones, counting the seconds played of the video. But here nothing at all gets tracked. I send it like this for the 25% milestone, whereas event16 should count the seconds and is defined as Numeric (Query String Parameter):
events: event11,event15,event16:14.3
It is defined in DTM in the Events section of the milestone like this:
event11
event15
event16="%custom-videoTimeDelta%"