Here is the response I received. They say they have no way of knowing if you made a purchase. I thought that is why I received and receipt and a lic. key.
Greetings.
Thank you for writing to us. Unfortunately at the moment we don't have a way to offer a discount for a new plane, based on the purchase of a different previous plane (this is partly a logistics issue because we don't have access to the private customer sales data from all of our resellers).
The X-Plane 10 versions of our planes can still be used mostly well in X-Plane 11 for now. However as X-Plane 11 continues to be developed the X-Plane 11 versions will receive free updates, enhancements, and new features.
Regards,
Carenado.