The record
A 1974 Environmental Health Perspectives paper stated that talc deposits include asbestos minerals that may carry over into consumer products, and that optical microscopy and x-ray diffraction analyses may not reveal their presence.
Claim scope
The method-inadequacy claim in the PEER-REVIEWED literature as of 1974 — the same year the industry was internally rejecting TEM on cost. This is the strongest possible support for the measurement-politics narrative because it does not depend on any internal document: the limitation of XRD was stated in the open literature, contemporaneously, in a PubMed-indexed journal. A companion paper, PMID 4470959 (Rohl & Langer, 'Identification and quantitation of asbestos in talc', Environ Health Perspect 1974), sets out the same conclusion at length: “Light microscopy is recommended for use only as a preliminary tool on limited, large-sized, samples. Transmission electron microscopy is a good standard technique for visualization of contaminant asbestos fibers.”
What this source does not establish
Not a measurement of any specific branded product and not a health study. PMID 31095409 quotes a further Rohl statement from the same 1974 volume about 10^9 fibers/mg at a 0.25% XRD detection limit; that specific quotation was verified only inside PMID 31095409, not against the Rohl paper's own full text.
Limitations
Both 1974 papers are PMC-open. Use these in preference to internal documents wherever the point is 'the inadequacy of XRD was publicly known', because they carry no litigation provenance.
Source
Pmid — 4470924