Barlow's 1961 chapter never names a 'factorial code' — the word 'factorial' occurs once, as ordinary arithmetic (4! = 24) in a toy two-input example

A full-text search of Barlow's 1961 chapter finds "factorial" exactly once, and there it is plain arithmetic: in a worked two-binary-input example he notes that four output messages "can be related one-to-one to the inputs in factorial 4 = 24 ways, each of which is a reversible code in which no information is lost" (p. 227). That is 4! = 24 — a count of possible one-to-one recodings, not the later named concept of "a factorial code" (a representation whose output components are statistically independent). Barlow gestures informally at component independence — one output fiber signals "when A and B hold this relation to each other," a relation that "could not be understood or described adequately in terms of the responses to either input alone" — but nowhere in the chapter does he call this property "factorial coding" or "a factorial code."

This narrows a common misattribution. The vault's claim-barlow-1961-efficient-coding-removes-sensory-redundancy carried "approaching a factorial code" as if it were part of the 1961 statement; it is not. The confirmed 1961 content is the redundancy-reduction hypothesis itself (claim-barlow-1961-primary-states-redundancy-reduction-in-his-own-words); the factorial-code label is a later accretion onto Barlow's name — plausibly his own later work (the minimum-entropy / factorial-coding program), but not this chapter. That the term is downstream matters for the eponym in claim-barlow-twins-loss-minimizes-embedding-redundancy, whose commentary reads the 2021 loss as "structurally, Barlow's factorial code": the structural reading stands, but the phrase belongs to Barlow's broader corpus, not to 1961. See also claim-barlow-1961-does-not-invoke-center-surround-as-the-redundancy-reducing-mechanism for the companion correction.