Dr.LipidDallas said:The answer turned out to depend on the detail I had left out of the opening post, which is a lesson about how to ask rather than about the subject.
I am going to disagree with the direction of travel here. The thread has converged on the tidiest answer rather than the best-supported one, and those are not the same thing.
Ask again with the specifics and you will get a better answer than this one.