Paithinasidharmasutra 5.11: Smṛticandrikā · Nirṇayasindhu · Mahānibandha +1

5.11

sapiṇḍīkaraṇād arvāg yāni śrāddhāni ṣoḍaśa | ekoddiṣṭavidhānena kuryāc chrāddhāni tāni hi

Those sixteen ancestral rites that precede the sapiṇḍīkaraṇa, / he should indeed perform those ancestral rites according to the rule for a single deceased.

The sixteen śrāddhas before the sapiṇḍīkaraṇa are to be performed by the rule of the single-person śrāddha.