Automation Question - Who will be sent an email?

Hello! I have a set of plan expiration reminder emails created to trigger close to plan expiration. Some are newly created, and I’m aware that automations are not retro active. How do I access the trigger data to figure out who will receive the emails so that when I set them up manually they are not receiving multiple emails?

I know that I can select the trigger to send once per person, but would that affect them getting the renewals in future years?

Thanks!
Erica