I saw this screenshot floating around for a California jury duty online questionnaire. Notice that "Not known" is a selectable option for one's marital status:
I don't know why someone's marital status would legally be unknown.
Under what cases would someone truthfully able to answer on a legal form that they don't know their marital status?
I can think of some possibilities that this field can be filled as unknown, such as if someone's filling in the form on someone else's behalf or if the filler has a mental disability. However, for the purposes of this post, let's ignore cases where one cannot recall one's marital status on their own, and only consider the case where it would legally be unknown.
I think one instance is if someone's working on getting their marriage annulled and doesn't know whether the process is complete or not. But are there other cases?