Two sources saying the same thing is worth something only if they are genuinely two sources. Most apparent corroboration is not.
Circular reporting is the commonest failure. Three news outlets report a fact; all three took it from the same agency wire; the wire took it from one official statement. That is one source wearing three coats. Follow every claim back to where it originated before counting it.
Aggregators are not independent. A dozen company-data services will show you the same directorship because they all ingest the same national register. Their agreement tells you they are all reading the same file.
A copy is not a second sighting. A document reposted elsewhere is the same document.
What does count: two bodies that produced their record separately, from their own processes. A shipping register and a port authority. A company register and a court filing. A photograph's own metadata and a second photograph of the same place from a different angle.
And when you cannot get two, say you have one. A single well-attributed source, named and dated, is honest work. Two dressed up as independent when they are not is worse than one, because somebody downstream will treat it as settled.