A marketing user pauses an Engagement Studio program and adds a new recipient list.

When a marketing user pauses an Engagement Studio program and adds a new recipient list, the newly added prospects will skip any Action steps the existing prospects have already completed, but will be evaluated on Trigger and Rule steps when the program is resumed. This is because Action steps are time-based and cannot be retroactively applied, while Trigger and Rule steps are condition-based and can be applied at any point in the program1. References: 1: [Engagement Studio FAQ]