Recent reports have suggested high-temperature superconductivity in pressurized La₃Ni₂O₇ (La-327), triggering intense interest in this bilayer nickelate system. However, establishing whether superconductivity is truly bulk and identifying its microscopic origin remains challenging. Accumulating evidence points to a complex materials landscape in La-327, including narrow phase stability, layer intergrowth, oxygen non-stoichiometry, oxygen site occupancy, structural distortion, and strain. In this talk, I will discuss how these intertwined structural and chemical factors complicate the interpretation of superconducting signatures. I will present our ongoing thermogravimetry (TG) and nuclear quadrupole resonance (NQR) studies of powder La-327, focusing how oxygen stoichiometry and local electronic environment vary depending on synthesis method, A-site substitution and partial oxygen pressure and temperature (pO₂, T) post-annealing history. This approach provides a materials framework for identifying well-defined La-327 candidate samples for assessing structural and chemical factors relevant to superconductivity.