Extending Your History
By default, the History palette stores only the last 20 steps that you’ve performed. When you perform more than 20 steps, the oldest changes are lost from the palette and you can’t access them to use them as a source for the History Brush. To change the number of history states that Photoshop retains, choose Edit > Preferences > General and set the number of History States to a value from 1 to 1,000. The larger the value, the more states stored—but on the flip side, you’ll be using more memory to store them.