Add a person to the 2 coalitions if s/he subscribes on another's subscription form

Since it is possible, with coalitions, to put another coalition's subscription on your coalition's subscription form, it seems that if a person subscribes on that form s/he should be added to both coalitions, not just the coalition that "owns" the form. For example, if the CYDsub coalition has a sign-up form that includes the YWI group's newsletter, when someone signs up on that sign-up form s/he should be added to both the CYDsub and the YWI coaltion databases.