My impression from styleguides etc is that the singular form is the newer one, and in some cases only somewhat begrudgingly accepted. E.g. recommendations that

My impression from styleguides etc is that the singular form is the newer one, and in some cases only somewhat begrudgingly accepted. E.g. recommendations that it is acceptable to use singular when writing for a "general audience", not in "formal or scientific writing", others referring to plural as "still in common use" (but singular taking over). But maybe there's been indeed a return to it in this specific field? not sure.