《晋书·志·第十章》
表明闰月在年外，那就不应该取闰月以越过周年忌日的重要祭礼，这是礼制中大祥期满除去丧服必用正式的周年的原因。 
明闰在年外，则不应取之以越期忌之重，礼制祥除必正期月故也。 
This indicates that the intercalary month is outside the year, so the intercalary month should not be taken to pass the important sacrifice of the anniversary of the death, which is why the period of great auspiciousness in the ritual system must use the formal anniversary to get rid of mourning clothes.