OK here's how it goes.
Each of the Service Committee has responsibility for things in "their" department.
Service Overseer oversees territory, mags and literature depts and usually has MS's and assistants helping out. Oversees "Trolley/Cart" ministry although the actual schedule will be done by a MS or another brother. Any of them might fill out forms but it is the responsibility of the S.O.
CoBE oversees Hall Servant and Sound Dept - now audio-visual (besides organising elders meetings, CO visit and most of the meeting schedules.
Secretary oversees Accounts (often done by another elder or a MS and he or the Sec can sort out charity tax reclaim forms), oversees (through group overseers) reports and sends "hours" to the branch. He looks after all the judicial records and child protection files and the policy (letters) file. Much of this is on line now anyway. Keeps minutes of elders meetings.