As I will mention again below, in both cases screen reader developers had to modify their product at the very basic level, after analyzing and even reverse engineering the application software. Here is my proposed definition of accessible application software. At least in retrospect, it is the obvious definition. Mouse usage depends on visual feedback of the location of the mouse pointer. Therefore blind people don't use a mouse to get to the tool bar, the radio button, the pushbutton, or whatever.
Accessible software includes keyboard equivalents for all mouse actions.
You have to be able to quickly, i.e., competitively, navigate through the application with the keyboard, using Tab and Arrow keys, for example. It's easy to check if keyboard access is available in an application - have the test team use the product without the mouse. Imagine using the tab key in a dialog, or the cursor keys in a text area, without any indication of where you are. It would be tough. Software which is accessible has a visual focus indicator that moves with the keyboard actions.