Psalms -> Psalm
When citing passages from the Psalms in some styles, it is customary to use "Psalm" as the book title if only 1 psalm is involved and "Psalms" only if there is more than one. Now, if all your references are to single Psalms, then one can use \setbooktitle{Psalms}{Psalm}
to make this switch, but if you have a reference to a series of Psalms in one place and a single Psalm in others, then you have switch back and forth. It would be nice if the internal logic could detect whether there are multiple Psalms in a citation and pick the name of the book appropriately.