Olsder's 1975 account of Song Jian's first exposure to population cybernetics contradicts Liang Zhongtang's 2009 dating of that exposure to 1978

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Liang Zhongtang's 2009 essay dates Song Jian's introduction to applying control theory and systems-engineering methods to population forecasting to a 1978 academic trip to Europe, and states that before that trip Song and his fellow rocket-engineering colleagues "had never heard that cybernetics and systems-engineering methods could also be used for population forecasting" (already recorded at claim-liang-2009-essay-corroborates-song-jian-1978-foreign-cybernetics-exposure). Geert Jan Olsder's own account states that in spring 1975 — three years before the trip Liang dates to 1978 — he described his University of Twente Systems and Control Theory group's Club-of-Rome-inspired mathematical population-growth research to Song directly, over a beer at the campus bar, and that "this work seemed to interest Jian immediately."

If Olsder's account is accurate, Song's first exposure to the idea of applying systems/control-theoretic methods to population modeling predates Liang's dating by three years — a specific, checkable contradiction between two sources on opposite sides of the vault's Song Jian causal-credit dispute, neither of which acknowledges the other. This is a genuine contradiction, not a false-friend pairing: both claims are about the same fact (when Song first encountered the method), stated in directly incompatible terms, and neither account was written with the other in view.

The contradiction is with Liang's no prior exposure clause specifically, not with his dating of the 1978 materials transfer. The companion note on the 1975 contact records that Liang's account of "the host" supplying "Song Jian and other guests" (plural) with materials in 1978 reads as a conference setting and is compatible with an earlier one-on-one conversation. What cannot stand alongside a 1975 Twente conversation about mathematical population growth is the sentence that follows it in Liang's paragraph — that before the 1978 trip Song and his colleagues had never heard of the method at all.

Both sources remain single-witness and unresolved: Liang's own 2009 essay is the only vault source for the "no exposure before 1978" claim, and Olsder's own 2024 recollection — of an event 49 years prior — is the only vault source for the 1975 visit. Resolving the contradiction would require independent corroboration of one account or the other, tracked at question-verify-song-jian-1975-twente-delegation-visit.