Best way to set up courses that need to be renewed every 3 months

Content

My client have a requirement for learners to complete Safety training every 3 months.  They have migrated data over from EBS and have one Course with multiple Offerings which are the ILTs set on different days.  

Eg

Course - Safety Training

Offering - 21 Dec Safety Training London

Activity - Day 1

Offering 2 - 21 March Safety Training Sheffield

Activity - Day 1 

etc etc 

We have the issue where if they are enrolled in 2 of the Offerings, the first has the status of Not Started, and the second, Pending Active.  Once the first Offering is completed, the second is automatically set to Deleted.