New JLBP? (Internal Libraries)

What should we say about libraries that are intended only for a specific project or projects? Examples:

* appengine-plugins-core (App Engine Maven and Gradle plugins, CT4E, and CT4I)
* plugins-login-common (CT4E, CT4I)
* Plexus (Maven)
* Sisu (Maven)

I'm not 100% sure that last two are good examples of this, but the first two certainly are.

These are libraries that are:

* Pushed to Maven Central as separate artifacts
* Change without notice
* not intended except for use by a small set of other projects maintained by the same or a closely related team