I'm not sure if citeproc-js can handle it, but did you try escaping the superscript HTML tags?
<term name="issue" form="short"> <single>n<sup>o</sup></single> <multiple>n<sup>os</sup></multiple></term>
We could indeed address identical values for editor & editorial-director in the same way, if a special label is needed for that case (J Jones, ed. & ed. dir. ?). Would only require a minor addition to CSL. Just let us know if it's required.
Can adjust ground to deal with it, but for a start, could you check the name elements in the specification, and indicate the category into which this one falls (i.e. fixed part of last name, dropping-particle, non-dropping particle)?
@Gracile: You can get "J. L." by setting initialize-with=".
Frank: But while we're here, could you check that you get the results you expect for the hyphenated case, when initialize-with is set to that value?
MHSmith: And J.-L. is correct (J-L. is a typo, obviously).
"And others": actually "et autres" is never used. Wouldn't it be better to substitute "et alii" (the long form, vs "et al.")
More important maybe: the verbal form for an editorial-director should be "sous la direction de" not "dirigé par".
There is one term I miss, probably because it isn't really used in English: "id." (feminine ead., plural iid./eid.), for the same author (citing a second title of his directly after the first one). [...]
PS Is your latest version online again?