Bak, Tang & Wiesenfeld's 1987 paper states, in their own words, that self-organized criticality's critical point is reached without tuning any external control parameter

self-organized-criticalitycomplex-systemsthresholdbak-tang-wiesenfeldsandpile-modelphase-transitionsource-discipline

Watkins, Pruessner, Chapman, Crosby & Jensen's 2015 refereed review, "25 Years of Self-Organized Criticality: Concepts and Controversies" (Space Science Reviews 198, 3–44; also arXiv:1504.04991), quotes Bak, Tang & Wiesenfeld's 1987 founding paper directly (Sec. 6.2, p. 381): an ordinary phase transition "can be reached only by tuning of a parameter, for instance the temperature," while self-organized criticality's critical point "is an attractor reached by starting far from equilibrium" whose scaling properties are "insensitive to the parameters of the model" — "no fine tuning is necessary."

This is a direct primary-quoted confirmation, rather than a secondary paraphrase, of the "no external tuning" property that claim-engineered-threshold-is-not-self-organized-criticality rests its central distinction on. It resolves the first half of question-verify-soc-no-external-tuning-necessary-not-sufficient: BTW's own 1987 wording, not a course-project summary of it, states that SOC requires no external parameter tuning. A Tier-3 UCSD graduate lecture note independently paraphrases the same point ("the claim by BTW was that this typical behavior develops without any significant 'tuning' of the system from the outside") — consistent corroboration, but non-load-bearing next to the direct quote above.

The original Phys. Rev. Lett. 59, 381 (1987) and Phys. Rev. A 38, 364 (1988) papers remain paywalled at link.aps.org with no freely accessible author-archived copy located; this note's Tier-1 status rests on the refereed review's page-cited direct quotation of them, not on an independent read of the originals.