The Union Civil War widow’s pension application indicated the soldier died in Memphis, Tennessee. Another document in the pension application indicated the soldier died in Springfield, Illinois. The soldier’s compiled military service record also indicated he died in Springfield. The document in the service record was created close to the time of his death–within a few weeks.
That’s more contemporary to the event than the documents in the pension file.
Generally speaking, for there are always exceptions, one wants to get a document that is as contemporary as possible.