In your role as a Fabric Analytics Engineer Associate, the task is to develop a DAX measure that calculates the average overall satisfaction score for a customer satisfaction report. This measure must fulfill several specific criteria:

1. Allow users to filter customer survey responses based on a selected product, thereby including only the responses of customers who have purchased that product.
2. Display the average overall satisfaction score from all surveys submitted in the last 12 months leading up to a selected date.
3. Ensure real-time data reflection as soon as the data is updated in the data store.
4. Include data exclusively from the current and previous calendar years within both the report and the semantic model.
5. Respect any table-level security configurations defined in the source data store.
6. Minimize the execution time of report queries.

Given these requirements, how should you complete the DAX code to achieve the desired outcome?