If my mother died on a different tithi (not Navami), should I still perform Matru Navami Shradh?

Yes. This is one of the most important aspects of Matru Navami: the Matru Navami provision applies to ALL deceased mothers, regardless of which tithi they died on. You should still perform your mother’s primary Shradh on her death tithi during Pitru Paksha — but Matru Navami (October 4, 2026) is ADDITIONALLY designated for all deceased mothers. Many families perform both: the tithi-specific Shradh on the relevant day AND Matru Navami Shradh on October 4.