The oldest copy is not always the most reliable. It may already be a correction, a translation, a misremembered recitation, or an imitation made with unusual care. To identify its age is to answer a question about its survival. To identify its authority requires other evidence.
We are nevertheless tempted by an original because it seems to promise an end to comparison. Somewhere, we imagine, a sentence exists before anyone misunderstood it. We could find that sentence and close the inquiry. The prospect is attractive for the same reason it should be examined: it would relieve the reader of responsibility for deciding between witnesses.
An order can sometimes be recovered without a trustworthy clock. A letter acknowledging an impression cannot have been written before the impression existed. A rubbing can preserve a correction that a caption denies. Such relations do not supply a universal chronology. They supply a sequence within the evidence, and that may be enough for the question at hand.
The third edition described by this catalog need not be older, cleaner, or more authoritative than the other two. It may be the name of a relation they permit us to recover. Its existence would then depend neither on an untouched sheet nor on agreement about an author. It would depend on whether another reader could perform the same reconstruction.