When you choose to display event between "3 month earlier and 3 month later", the jquery calendar is configured as following :

$j("#calendar-id").datepicker({
       minDate: '-3M',
       maxDate: '+3M',
       dateFormat: 'yy-mm-dd'
});

If the date of the day is the june 14th, the event between march 14th and septembre 14th will be displayed.

We want the events between march 1st and septembre 30th.

So the calendar should be configured with the specific dates:

$j("#calendar-id").datepicker({
       minDate: Date(01/03/16),
       maxDate: Date(30/09/16),
       dateFormat: 'yy-mm-dd'
});