I created a java procedure in order to update listbox content using a model.
This is the code, very simple:

public void listboxRenderer((List<MyData>) myList) {
    myListbox.setItemRenderer(listitemRenderer);
    ListModelList<MyData> listModelList = new ListModelList<MyData>((List<MyData>) myList);
    myListbox.setModel(listModelList);
    System.out.println("myListboxSize : " + myListbox.getItemCount());
    System.out.println("visibleItemCount : " + myListbox.getVisibleItemCount());
    for (Listitem item : myListbox.getItems()) {
        System.out.println(item + " - " + item.isVisible());
    }
}

This is the output:

-----------------------
availabilityListboxSize : 1
visibleItemCount : 1
<Listitem tYEQc4> - true
-----------------------
availabilityListboxSize : 1
visibleItemCount : 2
<Listitem tYEQz4> - true
-----------------------
availabilityListboxSize : 8
visibleItemCount : 10
<Listitem tYEQ16> - true
<Listitem tYEQ36> - true
<Listitem tYEQ56> - true
<Listitem tYEQ76> - true
<Listitem tYEQ96> - true
<Listitem tYEQb6> - true
<Listitem tYEQd6> - true
<Listitem tYEQf6> - true
-----------------------

It seems that after applying the model, visibleItemCount increases its value.