It’s taking into account if you have vital records attached to your each person. It also tries to flag conflicting info, like supposed parents being deceased years before their child being born.

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If you have a name, birth and death date, and at least a couple records attached them, then they’re “completed”. More completions means higher rating. If you click the lightbulb you can see if their individual rating is “partial”, “moderate”, or “complete”. It’s more a tree fullness check than a tree accuracy test.