If I am not wrong BB64 is still USS Wisconsin and not an ex-USS Wisconsin, isn't "ex" something you say about a ship that have been renamed?
Well, I have seen former Dutch warships, saying ''Ex- Hr.Ms. Mercuur'' as example. What means she used to be Naval service, and today as museum. HrMs (today ZrMs anyway) is carried by all active warships with militairy crew.