I should mention it shows the people killed in the "kills list" but not the history itself.
This indicates that you have your init settings set to cull unimportant historical figures. This is done to keep world sizes manageable and legends from getting clogged with historically insignificant people and events.
Someone who lived a prosaic life and then got killed by a vampire will be trimmed; she's not an unimportant extra during her life in worldgen, and the events of her life will be tracked identically to those of the mightiest heros while she lives, but after death the game evaluates her boring life and removes all specifics from the save. This means every event in her life, including her interactions with notable historical figures. Little to no evidence of her will be preserved in legends, and historical figures' histories will not show their interactions with her.
I'm not totally sure which events the game considers when trying to determine whether or not to cull a historical figure, but I'm pretty sure that combat, kills, night creature conversion, and migration are major factors, while things like job changes, marriage, and childbirth are not, even if the children do go on to become important historical figures (in which case one of their parents will be listed as "an unknown creature".)
I'm not sure if the game counts culled figures when it records the number of attackers, defenders, and casualties in historical battles, but I'm pretty sure that it does.
Animals with no kills likely don't get counted since legends mode accounts of fortress-mode battles only count animals as defenders if they have kills to their credit.