by Ken Task.
Not sure I can explain to anyone's satisfaction, but think new settings take affect from that time forward ... not backwards in time.
Will say that what controls is DB and certain tables - 3 to be exact.
This one: mdl_backup_courses however is the one you need to investigate!
The backup files you show appear to be where you can do something via command line to remove what you need by date ... something like
rm *20211114*
rm *20211115*
rm *20211117*
Leaving only the 19th's backup.
'SoS', Ken