Casualty recording is a discipline with published standards, and it is not the same activity as estimating a death toll.
A record, not a number. The unit is one person: who they were, where and when they died, and what is known about how. A figure with no records behind it cannot be checked, corrected, or used by anybody else.
Every record carries its sources. Where the information came from, when it was obtained, and how confident the recorder is. Two sources that both trace back to the same original are one source.
Duplicates are the main error. The same death reaches a recorder as a name, as a nickname, as a description, and as a hospital number. Merging records is a documented decision, not a tidy-up.
Say what the figure is. A count of documented deaths is a floor, not an estimate of the total, and reporting it as though it were the total is a misuse of your own work. Where a range is given, say what produces the range.
Do not publish what endangers the living. Names of survivors and witnesses, precise locations of people still in danger, and details that identify who spoke to you. A record that is safe to hold is not necessarily safe to publish.
Do not let a count become a claim it cannot support. How many died is one question; who is responsible is a different one, decided by a court on evidence, and a casualty record is not a finding of guilt.
Source. Every Casualty Counts, Standards for Casualty Recording, https://everycasualty.org/standards/ ; International Committee of the Red Cross, customary international humanitarian law database, https://ihl-databases.icrc.org/en/customary-ihl
What this is not. A method for attributing responsibility, and not a substitute for the work of a competent authority.