Sickness tracker with a rolling 12 months

Hi!
I have this spreadsheet which lists occasions of absence, and I'm trying to add a formula into Column G, which looks how many absences the employee has had in
the 12 months before the date of the current absence(given in Column D)? eg cell G10 would return the value 2, but cell G2 would return the value 1. Any ideas?
Thanks!
Sophie