Event emails

Hi

I run an event company and I want to create a flow of emails that the customer receives when they enter the event. The last email they will get is two weeks before the event date and is the most important (the others are news and offers from sponsors and tips etc)

The problem I have is that some people enter the event WITHIN the two week period BEFORE the event and will miss the date that I set in the flow.

How can I ensure that customers who do this can still receive the final instructions email without me having to send it manually?

Thanks in advance

Claire