We fabricate pwb's and face similar requirements. The solution we
came up with is daily samples and analysis( not the answer you want
to hear).
        You could sample the pot daily and only submit one per month. If
 you had a failure you could track back to the out of spec condition
 and recall only the parts run since  then.
       I don't know what your analysis costs are but the
liability costs  of once a month testing could be pretty steep.

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