Shared calendar is not listed when using CalendarApp.getAllCalendars() but found and accessible when using CalendarApp.getCalendarById()

Is there any reason why specific calendar would not be listed when using CalendarApp.getAllCalendars() ?

Example:

var cal = CalendarApp.getCalendarById( calendar ID );
Logger.log( cal.getName() );

var myCalendars = CalendarApp.getAllCalendars();
for( var q = 0 ; q < myCalendars.length ; q++ ){
    Logger.log( myCalendars[q].getName() +" > "+ myCalendars[q].getId());
}