If a parent died prior to February 16, 2021, and the Assessor does not become aware of the death until a year later and reassesses the property as of the date of death, are the parent-child exclusion provisions applied under Proposition 58 or Proposition 19?

The law in effect is that the date of death will apply. Proposition 19 is clear that Proposition 58 applies to transfers that occur on or before February 15, 2021, and Proposition 19 applies to transfers that occur on or after February 16, 2021.