Got that MJ - I used to know a bit about the MOR system.
It's the nomenclature that threw me, confused even on the CAA link.
In my simple mind something is either mandatory or it isn't, and in that world things mandated as reportable [CAS busts for example] would generate a "Mandatory Occurrence Report" (MOR).
However, they have come up with the wonderful:
Voluntary occurrence reports are also accepted under the MOR scheme. i.e. a report not required to be reported by the legislation but which the reporter believes should be brought to the attention of the CAA because of the safety implications.
Every day is a school day.