11 out of 119 controllers
this is also spin.
There might be that many across all the airspace groups that were affected by sickness that day,
but only a subset of the 119 - likely 15 to 20 odd in each case - would have the particular combination of ratings needed to replace the particular shift. Of those, probably 65% would already be at work that day, maybe 10-15% would be on holidays, leaving perhaps 25%, or maybe 4-5 people rostered off, who might have been eligible (fatigue wise) to fill the shift.
the other issue with this "overtime" is that it is SHORT NOTICE overtime - you usually get called only a few hours before AsA wants you to come in. If you've taken some medicine, had a drink, or just not had enough sleep, you are not fit for duty, and so you cannot attend - no matter how much AsA might want you to.
If we had a policy of overstaffing - or even an actual "on-call" type roster, then there would be less of a problem. But one of those needs extra staff, and the other needs advance planning....