Three links.
One source.
A claim can gather an impressive collection of links without acquiring any new evidence.
Imagine finding the same statement in three articles. The first links to a report. The second quotes the first. The third summarises the same report. You have found three pages, but they do not give you three independent checks of the statement.
They may offer useful context or different interpretations. The important question is what each one actually adds.
Follow the trail once.
Open the references until you reach the document the claim depends on. Look for an original study, filing, dataset, interview or other primary record where one is available. A primary source can still be incomplete, mistaken or limited; reaching it gives you something more specific to inspect.
Compare the passage with the sentence you plan to use. Do they describe the same people or things, the same period and the same measure? Keep any condition that changes the meaning.
Ask what changed at each stop.
Did a later article obtain new evidence, or only rephrase the earlier one? Did the writer interview someone else, check another record or add a relevant comparison? A different publisher does not, by itself, make the underlying evidence independent.
There is no need to discard every secondary source. A good explanation can help you understand a difficult paper. Just keep the explanation and the supporting record distinct in your notes.
Leave a note someone can use.
Record the original source, the exact passage and which later articles rely on it. Add the reason you think the passage supports the claim. If the original is inaccessible, say which version you could read and leave that limitation visible.
The free source-note worksheet gives you a place to keep the claim, passage and your assessment together. It runs in the page and downloads a Markdown note. Save the note before closing it.
A source trail is useful when the next reader can follow it. That reader might be your editor, a colleague, or you next Tuesday.