The Misfits have been second-years for a while, since the Hearbreaker arc was about them coaching the new 1st years (like Chima and Silvia).Took around 400+ chapters for Iruma to go from 1st year to 2nd year. This means we will have around 2000+ more chapters for Iruma and friends to reach the final 6th year of the curriculum.
This is the class entering their 4th semester at Babylis, out of a minimum of 6 and up to 12. Perosnally, I expect to see them become 3rd years, with the big conflict happening during their 6th semester.