Sometimes a customer would ask us, "Because our SMEs are not ready, can we move the iteration review date out a few days or a week?"
Then we spent some time reminding them that one of the most effective parts of the Lean-Agile approach is that the development team has a consistent cadence or pace to work. We explained the impact of delaying the courseware deliverable date and reminded the customer that if we need to shift some of the specific work items from iteration #2 to iteration #3 we can do that to accommodate the SME availability without breaking the fixed time box iteration mechanism that provides the beneficial cadence to the development team. The customer was okay with us moving a few work items those SMEs needed to be available for to another iteration and bringing forward some of the work items from the next iteration instead.
We held the iteration demo with all the working-ready-for-demo work items, did not demo those work items that were unfinished and moved to another iteration.