The Difference Between A Source And A Page That Copied One
Almost everything you read is a copy, and copies drift.
Every fact you encounter is somewhere on a chain. At one end is the place the fact was created: the measurement, the decision, the record, the document that first stated it. Everything else is a report of that, or a report of a report, and each step introduces the possibility of compression, error, misplaced emphasis and quiet embellishment. Most of what any of us reads sits several steps down this chain, and the steps are invisible, because a page that copied a source and a page that is the source look identical when they are rendered on a screen.
Learning to feel where you are on the chain is the core skill of judgement. The signs are readable once you look for them. Original material tends to be specific, boring, hedged, and burdened with detail that no summariser would bother to keep: exact scope, conditions, limitations, the awkward parts. Copies are fluent and confident. They round numbers, drop qualifiers, and state as fact what the original stated as an estimate under conditions. Fluency is not a sign of reliability. Very often it is a sign of distance from the thing being described.
The practical response is a habit rather than a verdict. When something matters, ask where the page got it, and keep asking until you reach something that could not have got it from anywhere else. Sometimes that takes one step and you find yourself reading the actual decision or the actual record, which is usually clearer than any account of it. Sometimes you cannot get there and you have to decide how much weight to put on a claim of unknown parentage. Knowing which of those two situations you are in is most of the value.