I deduce you are only interested in the USA scenario as a support mechanism.
Regret I don’t have any definitive answers to yr queries.
One purely textual possibility may be related to interpretations of the word “intended” in yr quote.
Regarding recalls due to metal contamination, don’t forget that manufacturers / distributors have responsibilities for both safety and non-safety defects in their products / labelling as per the product specification. I presume a supplier-initiated recall could be related to a perception of either / both, ie “damage limitation”.
Subtler aspects of “adulteration” might also be (supplier) considered of possible future consequence, for example this (2003) extract –
Not all foreign objects are physical hazards. For example, tiny metal shavings sometimes generated by opening cans with a can opener do not normally pose a physical hazard. Other types of foreign objects that are not categorized as physical hazards include insects and mites and their fragments, evidence of rodents and birds such as their excreta, hairs and feathers, and molds and rots associated with decomposition and dirty machinery parts.
Foods containing these types of nonhazardous foreign matter may be deemed adulterated under Section 402(a)(3) of the FD&C Act in that ‘‘it consists in whole or in part of any filthy, putrid, or decomposed substance’’ or ‘‘it is otherwise unfit for food.’’
(Food Plant Sanitation, Hui, 2003)
It seemed to me that my quote in yr earlier thread is one example of an attempted “flexible” FDA haccp interpretation, ie
B. Your HACCP plan for seafood salads at the "Vegetable Processing" CCP lists the critical limit of "No metal particles in excess of (b)(4) mm". This critical limit is not adequate to control metal fragments that may cause trauma or serious injury. FDA recommends a critical limit at metal detection of "no detectable metal fragments" because foreign objects that are less than (b)(4) mm may cause trauma or injury to persons in special risk groups, such as infants, surgery patients, and the elderly.
( AFAIK, USFDA have only initiated direct [safety] action where a non-compliance with the 7mm criterion was involved. But then again, this may also be due to the other manufacturer alternatives as noted above ).
Regarding rationale, I noticed this convenient but perhaps rather simplistic, non-medical guideline -
Smaller objects (2-6mm) are only a danger for people who depend on the care and attention of others for their food and drink; this is the case of small children, the ill and the elderly.
(Principles of Hygiene and FS Management, PIP, 2011)
I still anticipate that the 1st Olsen paper probably has the best technical answers.
Rgds / Charles.C