Help with superposition
There are times you ought to apply source transformation when solving with superposition, instead of attempting these shortcut you've shown above.
Source transformations allows you to move resistors in series or parallel with a source, opening space for simpler and less prone to error mathematics. 

For example, in the first instance of removing all but 9v source.
You tried a shortcut but for some odd reason neglected one 500 ohm resistor, and thought you could add the 500 with the 250. Also you can't add 50 with 200, with respect to  (A) + and (B) -, because they are parallel with respect to that thevenin.

You should try to convert transform the voltage source to current source, after adding 150 and 350 ohms in series. So you can have 500 ohms in parallel with the other 500 ohms, to truly calculate the next resistance in series/parallel. Then again transform the source from current source to voltage to continue. etc... 

Here's the basic idea of transforming between current and voltage source


Here's a demonstration, without giving the final answer of one of the instances.