No.5 B.F.T.S. Courses
VQ5X03
It looks like your Dad did something similar to my Dad, i.e. arrived with one course but qualified on the next course.
My Dad arrived at Clewiston with Course 11. 25/09/42, fell ill and was placed on Course 12. when he recovered.
Course 12. arrived Clewiston 12/11/42 (so that is where your Dad arrives) but Course 12. qualified 25/5/43, so, as you say that your Dad left Clewiston in July 1943 he must have qualified with Course 13. on 30/07/43.
Ian BB