quite a large spreadsheet - so rather than work through that - perhaps a small sample or explanation

you can do a rolling 6 mths using TODAY(), when you open the sheet

assuming on calendar sheet
Sickness - you are adding instance and days - I assume again -
using
=COUNTIF(Table2[@[Column2]:[Column367]],"SCs1")+COUNTIF(Table2[@[Column2]:[Column367]],"DCs1")
maybe not as i can not enter "SCs1"
but something like
COUNTIFS ( ...... , date range ,,">="&DATE(YEAR(TODAY()),MONTH(TODAY())-6,DAY(TODAY()))
Not i have -6 on the months to go back 6 months from today