Many police department don’t report the deaths of people due to their actions or in their custody to any sort of national database as well, so estimates are likely undercounting. Corruption is rampant in departments as well, there have been cases of people dying and being buried by police without informing the family or anyone else.
So it’s likely much worse than we realize. Many murders are unsolved, there are many missing people cases also unsolved. In 2020, there were dozens of people reported missing that were involved in protests that were never found.