No source was found documenting an explicit comparison of Heuer's ACH to expert-system backward chaining; the resemblance remains an observed structural echo

The commentary on claim-ach-step-5-instructs-analysts-to-disprove-not-prove noted a structural rhyme between ACH's Step 5 (enumerate hypotheses, then work to eliminate them) and backward chaining in 1970s expert systems — goal-directed elimination developed in the same decade as MYCIN and DENDRAL — while declining to promote the rhyme beyond an "observed structural echo" absent a primary source. A targeted search for that primary source found none.

Three sources were checked: Heuer's own account of ACH's foundations, the CIA's institutional history of how Heuer developed ACH, and the one AI-adjacent paper that formally reformulates ACH's logic. None draws or references a comparison to backward chaining or expert systems. This is stronger than "nothing was findable either way": two detailed Tier-1 primary accounts specifically narrate ACH's intellectual lineage and are silent on AI where such an influence, if real, would plausibly have surfaced.

The finding is bounded, not conclusive. Heuer's personal memoir (Rethinking Intelligence, 2018) and a paywalled academic review (Dhami 2019) were not accessed — see question-ach-backward-chaining-structural-echo, which stays open to track those unread sources. Within this search's scope, the ACH ↔ backward-chaining resemblance is best characterized as an [unverified — could not confirm or deny after search] observed structural echo, not a documented or acknowledged lineage.