What is the difference between Purnima Shradh and Sarvapitri Amavasya?

Purnima Shradh is specifically for ancestors who departed on Purnima Tithi and marks the opening of the ancestral fortnight. Sarvapitri Amavasya, on the last day, is a universal Shradh covering all ancestors regardless of their death tithi. Many families perform both to ensure comprehensive ancestral rites.