I have no idea why your boss would wish to exclude a recent absence in the disciplinary review - even less as to why you'd choose to remind him.
Just to be clear about this, discplinary proceedings are initiated after a combination of occasions of absence, coupled with the total number of days. 6 occasions of one day each (especially if on a Monday) are often regarded in a worst light than one occasion of 6 days' duration.
Different company policies vary - provided the policy is applied consistently across all employees and does not disciminate generally accross one group (pregnent women, say).
Also sickness is one of the reasons for absence - it isn't 'special', and if absence one cannot do one's job. Therefore all absence - sickness, authorised LoA and unauthorised are typically lumped together in counting the number occasions.
Since you've had 6 occasions in the last year and the trigger point for your company was 3, you are fortunate not to have been disciplined before. Maybe your boss was being kind to you. Maybe he should have taken action before and failed to. Maybe that's why he didn't want his boss to realise that there was yet another absence to add to the stack prior to him initiating action.