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"I would love to know the basis for PSR's assertion that some matchlocks were still in front-line use up to 1708."
Me too. According to the following article which contains a chapter on the transition from the mousquet to the fusil (pp.101-103) the whole French infantry was equipped with flintlocks by 1703.
p. 103: "Le 1er octobre 1703, une ordonnance supprime les dernières piques et, cette même année, l'usage du fusil à baïonnette à douille sera devenu général dans l'infanterie française."