W3schools offers a better explanation on the ready-state-change
here.
To answer your question in particular, it cannot be determined. While transitions between states are defined certain states may trigger the on-ready-state function multiple times (e.g. 3: processing request ).
Note - W3schools mentions that "onreadystatechange event is triggered four times, one time for each change in readyState.", but I remember of some place that onreadystatechange could trigger of multiple times, for the same state.
Usually there is no interest in the other states and the only state that is important is readyState==4 and status==200. Using a Javascript library JQuery, Prototype even hide this and give you simple function to work with like Ajax.Load('page', element)