Siobhan was not used in
France until 1980s, after 1981 (the statistics show 1988 as the first year with a minimum of three girls named
Siobhan) and, even since then, the use has been purely marginal (less of seventy girls named
Siobhan).
After the law 11 germinal, an XI (
April 1, 1803), it was forbidden to pick a name outside an official list of names (that was, approximately, coincident with the saints' list); it was, then, impossible to use
Siobhan in
France (if some parents could have known it in a trip to
Ireland, for example). The law was modified in 1966 to include several mythological names, regional names, compound names and some variants and diminutifs, but not foreign names; again,
Siobhan was impossible.
I cited 1981 because then the law was again modified in order to accept, among others, foreign names.
As you pointed,
Siobhan is not credible at all as name for a French girl in the 19th c.
Lumia
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