May have/Might have and Must have: Modals
by “May have and might have” are used to express the possibility or chances of work being done in the past.
Might have–20 to 40% guess of something means chances were less to complete the task. “Might have” used for a complete guess or speculation for the past situation.
May have–50 to 60% chances of doing work. It shows more chances to complete the job.
Must have ¬-
It makes sure that action takes place with strong affirmation. It is sure that action definitely happened.