What happens when my default access model is not available for a triggered DDA purchase?

If access model selected is not available, purchase hierarchy is: Non-Linear, Unlimited, 3-user, 1-user
For example, if your default is Unlimited and the title is not available as Unlimited, the system starts at the top of the hierarchy, purchasing Non-Linear if available
If Non-Linear is not available, the system progresses through the purchase hierarchy until it finds an access model that is available