Langlois & Seignobos's 1898 External/Internal Criticism split names the same two-axis architecture as the Admiralty Code and RAG, with Mabillon's diplomatics as its authenticity-axis toolkit

bridge-investigationdiplomaticshistorical-methodintelligence-tradecraftRAGmabillonlanglois-seignobosexternal-criticisminternal-criticismmultiple-discovery

Langlois and Seignobos's Introduction to the Study of History (1898; English translation 1904) — the founding methods manual of professionalized academic history — divides all historical-document evaluation into two sequential operations: "The first group of preliminary investigations, bearing upon the writing, the language, the form, the source, constitutes the special domain of External Criticism, or critical scholarship. Next comes Internal Criticism: it endeavours, by the help of analogies mostly borrowed from general psychology, to reproduce the mental states through which the author of the document passed. Knowing what the author of the document has said, we ask (1) What did he mean? (2) Did he believe what he said? (3) Was he justified in believing whatever he did believe?"

This is, at the level of abstraction, the same shape the Admiralty Code splits into source reliability vs. information credibility and reliability-aware RAG re-derives as source reliability vs. relevance, already synthesized in observation-intelligence-doctrine-and-rag-independently-derived-a-two-axis-source-model: is the document/source what it claims to be (External Criticism / reliability), judged apart from whether its specific content is believable (Internal Criticism / credibility). External Criticism's own stated territory — "the writing, the language, the form, the source" — is exactly the evidentiary ground Mabillon's 1681 diplomatics works, and the same ground Gates's 2025 Altair BASIC authentication occupies as a modern diplomatics-cluster instance: judging a document's own genuineness from internal, hard-to-fake features, prior to and separate from any question of whether its content is credible.

This identifies a textually-documented common shape, predating the Admiralty Code by roughly four decades and RAG by 127 years — not an established common ancestor. It is consistent with, and does not contradict, the vault's existing finding that the Admiralty Code's 1939 origin shows no documented contact with historical-method or diplomatics scholarship and with diplomatics's institutional-absorption-not-derivation status in 19th-century historiography: the same abstract problem appears to force the same two-part solution onto independent fields, repeatedly, without a demonstrated transmission chain between any two instances of it.