Quick response ...

I don't follow what the words of the argument are supposed to be (I'm
guessing it's not English ... perhaps "Le flegmatique" from the
French?), nor do I follow the exact positions. But most importantly,
I'm not sure I follow what part of this is important, from your point
of view, to retain. If you were not interested in precise positions,
original lineation, and on what page something was found, just

      <argument xml:lang="fr">
        <p>Le flegmatique.</p>

would do. But (because you bothered to ask), I'm guessing that at
least pagination and lineation matter. In which case,

      <argument xml:lang="fr">
        <p xml:id="ap01" next="#ap02">Le fl</p>
        <p xml:id="ap03" next="#ap04">matiq</p>
        <pb sameAs="#pb15"/>
        <!-- where pb15 is the page break in the main text -->
        <p xml:id="ap02" next="#ap03">eg&#xAD;</p>
        <p xml:id="ap04" prev="#ap03">ue.</p>

will probably do the job. But if you also want to encode each bit
close to where it actually occurs in the text stream, it gets a bit
tougher, as <argument> is only allowed at the beginning of <div>
kinda things.