If you're setting the text inside Animation Composer it overrides the text layers inside the precomps.
If you would like to edit the text layers inside you need to use "Pull from Primary Comp" feature in After Effects. Here is where to find it:
Setting the text inside Animation Composer allows you to have different texts on each layer, but you loose the ability to make parts of the text bold. This is something we would love to add in future versions.
Here is a video showcasing how it works: