Agree on most points.
It's not that difficult. Based on an agreed formula, say the Bradford Factor. ("The Bradford Factor formula itself is: S² x D = B. This means that the number of spells of absence (S) is multiplied by itself, with that number then multiplied by the total number of days a person was absent (D) during a 52-week period") Agree a 'score' that triggers the Absence Management framework, ie improve attendance or will be managed out, usually via a Capability Policy. (If you're not there you're not capable of doing your job, irrespective of your talent.)
Same 6mths+6mths in much of the finance sector, but with MUCH lower sickness levels. Reason - see my previous paragraph.
Should it exclude these? It's not a matter of whether the sickness/injury is genuine, its the fact that if you're not there then you can't do your job. Obviously I would hope that some level of discretion/humanity is shown, but the default attitude should be that the civil service is not a charity.