Fanfictions about the Lamenters contribute to the overall lore by presenting different interpretations of their abilities and culture. Writers might come up with new ideas about their combat tactics, their religious beliefs, or their relationships with other Space Marine chapters. This diversity of ideas enriches the Warhammer 40k universe as a whole.
Isha also contributes by adding a layer of mystery. Fanfiction writers can explore her powers and limitations. Her powers, which are related to nature and life, can be a driving force in many stories. For example, a story could revolve around a human scientist who discovers a new form of energy that he believes is related to Isha's power, and he tries to harness it for the good of humanity.
They fill in the gaps. There are many details in the 'Horus Heresy Short Stories' that add to the overall lore. For example, they might explain certain events that led up to the main Horus Heresy conflict. They also provide more backstory for characters that we might only see briefly in the main Warhammer 40,000 narrative.
Lore can be seen as the back story. It might include details about the origins of a place, the past of characters, or the hidden histories that shape the current situation in a story or game.
The Warhammer series and Warhammer 40000 series were both very popular fantasy novels and game series. They had their own unique styles and playstyles. Which one was more playable depended on one's personal interests and game preferences.
The medieval warhammer series included many books and games, which included a large number of role-playing, combat, and strategy elements. Players could play different roles such as warriors, mages, thieves, etc. through combat, leveling, and exploration to continuously improve their abilities. The series also included rich historical backgrounds and fictional worlds to make the game more interesting.
The Warhammer 40000 series focused more on the grand world view and war simulation. Players could play as a member of an empire or race in the game and participate in the wars and adventures of the entire Warhammer world. The series contained a large number of NPCs, monsters, and scenes, as well as complex missions and plots, making the game more challenging and deep.
If you like role-playing and strategy games, then the medieval warhammer series might be more suitable. If you like a grand world view and war simulation, then the Warhammer 40000 series might be more suitable. Of course, everyone's interests were different. They could choose their favorite game series according to their own preferences.
The Lore TV show is indeed fictionalized. It takes elements from various sources and weaves them into fictional narratives that may or may not have real-world inspirations, but are not based on actual events.