Well there is a big difference between a private variable, and a global.
If you change a global variable that value will be the new value in other layouts. If you change a private variable that value will revert to its initial setting..... unless you make the object that the private variable belongs to global.
You see not all objects are necessarily global, but all are usable across all layouts.
I should mention you will probably need to copy and paste an existing object into another layout in order to use it.