Was listening to David's latest video on YouTube tonight regarding the Valkyrie/Gordian Protocol Series. In it he was talking about the background and original concept for the series. I suspect much of this has already been hashed out here but I was struck by the way he described it.
In his description of the series as having an original concept of being a police procedural in time travel I was reminded of the Paratime series of stories by H. Beam Piper. These were about the Paratime Police patrolling different timelines to try and keep the "Home Timeline" safe and unchallenged in its monopoly of time travel. In many ways resembling a Victorian era British Empire analog.
Also David's description of the two main ways scifi authors use the concept of either time travel/multiple universes reminded me of Piper, and to be honest David's own usage in the Apocalypse Troll and the WarGod series. The first way of dealing with multiple universes is that for every decision point that might break off a new timeline all options that might occur do occur but the observer only can see the one that from his perspective continues. However the alternate decisions that would break off a new universe also occur and the alternate universes proceed from there. This comes closest to the concept Piper used and also the "Many Universe" theory David used in Apocalypse Troll I believe.
The other way David described of how to deal with this is that at the decision point only one decision occurs and you end up with a new timeline/universe budding off the main universe. From my understanding this is how he and Jacob are planning on framing this series. Also I believe this is close to how David uses this concept in the WarGod series where there are multiple potential universes with different outcomes but, at the decision point, once the decision is made the other outcomes cease to exist from the main universes viewpoint.
I wonder if David read H. Beam Piper and if the themes in the Paratime stories, including the Lord Kalvan stories, percolated around for years to provide sparks for his story telling.