Chapter Approved

As a reference, each Index books point cost section will list the factions that are available, and each Index may feature armies with specific common keywords that can be taken as well like 'Chaos' or 'Aeldari' or 'Imperium' or 'Adeptus Astartes' or ‘Thousand Sons’ just to name a few.
Such armies use up all the factions they are comprised of, and as such those factions will be unavailable to other team members.

It is OK to have two or more armies with an overarching keyword (for example Chaos or Imperium) as long as factions do not get repeated within a team.

Please note that some models have keywords across factions like the Ministorum Priest, who has the Adeptus Ministorum and Astra Militarum keywords. Models like that only take up the faction slot for the Detachment they are actually taken in. For instance, a ministorum priest taken in an astra militarum army does not take up the adeptus ministorum faction slot for the team and vice versa. This also means that a Priest can be taken in both an Astra Militarum and an Adeptus Ministorum build for the team, but also implies that if this model is taken in a
detachment with the Imperium as common keyword, it can no longer be used in either an Astra Militarum or Adeptus Ministorum build for another team member.

Pour la question du Chapter approved, je dirais que cela dépend surtout de quand on rend les listes. Si c'est genre 3 jours après, c'est trop tard. Chiant, mais trop tard. Si on parle de 3 semaines, cela peut se faire.