Tritiya Shraddha is the third day of Pitrupaksha, it is the third day of Mahalaya Paksha. Tadiya Shraddha is another name of Tritiya Shraddha. The tadiya or Tritiya Thithi of the Krishna Paksha of Bhadrapatha Month is known as Tritiya Shraddha. https://www.vinaybajrangi.com/hindu-rituals/why-shradh-is-observed-in-ashwin.php