We ask not merely whether layer birth occurs, but how many primitive kinds of birth are experimentally accessible. Within the Six-Birds framework, birth events can be organized by activation of packaging (P5), directed circulation (P6drive), and staging anomaly (P4). We show that these primitives support a small canonical taxonomy of four layer-birth classes and that the corresponding classes can be operationally instantiated and separated in a common measured observable space. Class-I activates packaging without drive; Class-II activates packaging together with directed circulation; Class-III activates packaging together with a staging anomaly but without drive; and Class-IV activates all three. The strongest empirical separation is between Class-I and Class-II, where affinity at structural birth robustly discriminates drive-free from driven births and explicit no-fake-arrow controls rule out coarse-graining artifacts. We then place all four classes on a shared observable map using structural boundary location, affinity at boundary, and a strict-rule-aligned staging proxy. Capacity/depth behaves as a post-birth field rather than a primary classifier, and at least one upstream/PICA-style system can be embedded in the same coordinate system. We do not claim stabilized universality exponents. Instead, we provide a primitive taxonomy and observable separation of layer-birth classes that future universality work must respect.
Ioannis Tsiokos (Mon,) studied this question.