A pile of a thousand documents is not automatically a corpus in any useful sense; it becomes one only at the point someone can move through it purposefully — find a specific text, trace a theme across several, compare a claim against its variants — rather than merely knowing, in the abstract, that the documents all exist somewhere. Corpus legibility is the precondition for corpus knowledge, and it is frequently underinvested relative to corpus accumulation, since gathering material feels like progress while indexing it feels like maintenance. FormatAdmission names the threshold at which material acquires enough formal structure to enter retrieval, comparison and synthesis: a corpus becomes available to readers and machines only when its internal organisation supports later, non-linear use. An unindexed archive is not a smaller version of a legible one; it is a different, much less useful kind of object.