|=====|
|=====|      there are identical in ID_3 and count as 3
|=====|
        |=====|
               |=====|  and these two are again 
                                 in ID_3 but there are not
                                 Identical so they have different
                           counting as each of them count as one!
and 
when 
|=====|
             |=====|    they do not have 2bp overlap
                                 the ID will change to ID_4
as you see in ID_3 all of them had 2bp overlapped