at least in my dim understand of them, Phil --of course, it's hard to believe that any terms in French would be "vague."
"chevet: eastern end of a church"
normally, only one "eastern end" of anything, last time i looked.
the Britannica reference is, of course, wrong --churches with two "working ends" (my technical, precise term) are not uncommon, in Ottonian Germany and regions of France which were influenced by that architectural tradition (like Verdun)
http://www.abelard.org/france/culture/lorraine/plan_cathedra...seems to me that what we may be dealing with here is something with a rather unusual ("non-standard") design, like at Metz
http://www.abelard.org/france/culture/lorraine/metz_plan.pngwhere "les fonds [sic] baptismaux" might be seen in one of those "chevets Ouest" --*if* we allow for the misuse of the term "chevet" in place of what those western thingies are, which is simply chapels off of the southwestern side aisle of the nave.
to my sensibility, a "chevet" cannot be applied to just any structure which terminates in an "apse."
but, that's why i would love to see a plan of this building, to determine how imprecise the author's nomenclature is.