@theluthier The "Hair Density Texture" is working this time without "Children Hairs" because you assigned that texture before combing the hairs in "Particle Edit Mode" so that the texture affects the hair growth. No hairs exist in 100% black painted areas of the "Hair Density Texture" and the view is the same in "Object Mode" as well as in "Particle Edit Mode".
As soon as you edit the hairs in "Particle Edit Mode" the "Particle Simulation" no longer controls the hair growth and the appropriate settings in the "Particle System Properties" are greyed out.
In the case of the first layer of body feathers, you first combed the hairs and only then assigned the "Hair Density Texture" so that you needed to activate "Children Hairs" in order to remove hairs in 100% black painted areas of your "Hair Density Texture". But this only makes these hairs invisible in "Object Mode", whereas they still can be seen in "Particle Edit Mode". These hidden hairs nevertheless still influence the calculation for the "Interpolated Children Hairs".
Please also see my post here with screenshots.