Good names! But the gist is basically this – we have essentially two core books: Core Combat Rules, and this one we currently call ‘Players Guide’. Each of these branches off to more specialized sourcebooks.
Core Rules is linked to the two weapon books: “Weapons of the Ancient World” I and II (II covers armor and missile weapons). In the future it may also link to books on cavalry or siege warfare.
“Players Guide” gives the basics on Character Generation, Magic, and campaign settings. For more detail on magic you have Superno, for more on the campaign settings you have the two Medieval Baltic history books, plus the Codex Adventum series starting with the Road to Monsterberg. The more in depth character generation book isn’t done yet but will be called Codex Ingenium. A lot of what is in Ingenium has in fact gone into “Players Guide”, but in a simplified format.