1. If you are personalizing first name & last name from the Recipient table. Then seed address first name & last name should be present. If the field value for first name & last name is empty in the seed address then random values will be personalized at the time of delivery.
2. If you are personalizing the first name & last name from targetData then you need to define that field in the seed address Additional data tab. This will work in normal delivery & not in a recurring delivery. Also in the workflow, you need to add the alias for the respective column starting with @ for example @firstName.