But only one of them, Big K, defines the kilogram. So the ones losing mass might just gain mass more slowly than Big K. Or they might even all be losing mass bu

But only one of them, Big K, defines the kilogram. So the ones losing mass might just gain mass more slowly than Big K. Or they might even all be losing mass but some more slowly than Big K making them apparently gain mass. I don't know if we know how the masses actually changed.