Graphs: New data does not update properly

Using the built-in spread sheet to update an existing graph will usually work erratically (it usually tries to "snap back" to something akin to what the graph looked like before it was styled) or stop working altogether once there has been significant styling done to the graph such as changing the proportions or altering manually the "look" of the graph elements. Also, since the graph feature goes back to the 1990s with little or no updating many of Illustrator's later features don't even work with a graph. For example you can't use the Transform Panel to change the height or width of any element of a graph. When you click on any graph element the Transform Panel will be greyed out.

What I usually do when using the feature is keep a copy of the graph as it's first created with all strokes and fills set to "None". I then put the now "invisible" copy somewhere outside the artboard. If I need any changes done to a graph that is no longer controlled by the spread sheet I can then switch to the Outline mode—to see my "invisible" copy—and apply the changes to it. I can then apply the changes manually to the stylized version using my invisible copy as a template. Since you don't actually have the earliest versions of your client's graphs, I realize that the information I'm giving may not help very much at this point.