Amavasya Tithi Shraddha (death anniversary) is done for those deceased family members who died on Amavasya Tithi, Purnima Tithi and Chaturdashi Tithi.
If someone is not able to perform shraddham [death anniversary] on all tithis then single shraddha (for all) on this day is enough to appease all deceased souls in the family. If death anniversary of ancestors is not known or forgotten then those shraddhas can be performed on this tithi. That’s why amavasyais also known as sarvapitra moksha amavasya.
