When is the Extension section in a horizontal pattern executed?

The Extension section in a horizontal pattern is executed after the Identification sections have completed and the CI has been identified. The Extension section allows adding additional attributes or relationships to the CI, or launching other patterns for further discovery12.

References:

1: ITOM: Extending Discovery/Service Mapping Patterns - GlideFast ServiceNow

2: Horizontal Pattern probe - Product Documentation: San Diego - ServiceNow