I read Music Licenses, FAQs and Standard License (all were helpful to me)
ALL things in the series (eg episode, edition) must be connected
I suppose, if all videos are about the same game, then it’s legal.
I think term “series” should means a historical connection. All episodes in the series must have a single storyline and connected by plot. They are watched one by one, starting from #1 and ending with #20 (Not coincidentally episodes are numbered). So, the series could be a single continuous video, but because of its great length, it’s just divided into episodes. That’s why series considered a single End Product.
Example of series: walkthrough of one game.
It’s only my opinion, may be wrong.
Honestly, I don’t quite understand too. This FAQ clause is slightly ambiguous for me.