I think what is happening is that you have created different panel files for each of your iPads from one master file, then modified the Smart Graphics objects slightly. Then when you import them into Simpl Windows, it tells you that this is a newer version of the original file and changes all the file names to match the one you just imported. If that is the case, there is a check box that needs to be checked when you do a Save As that will unlink the Smart Graphics extenders from the previous file. When you do this, Simpl Windows won't see them as all the same and will allow you to use multiple panel files.
If that is not what is happening, then Steve is correct. The Smart Graphics extenders for each panel get associated with that panel's IPID, so that pressing the number 1 on a keypad on one panel won't trigger the number 1 on a panel that is using the identical file.
If you are using the same SG objects on multiple UIs then all you need to do is import one set of objects for all of your UIs and then define your signals on the Simpl side so they are unique for each UI
Here's a screenshot of the dialog I'm talking about.