The guest count moves: the one number every event argument is about

Three deadlines, not one

Clients hear "final numbers" as a single date. A venue has at least three: the point the count is used for the room plan, the point the kitchen orders against it, and the point after which nothing can come off the invoice. They are days apart and they exist for different reasons. Publishing all three, with the reason beside each, converts an argument about fairness into a conversation about a calendar.

Up is a different problem from down

Adding ten guests is a capacity and staffing question with a hard ceiling; removing ten is a cost question with a contractual floor. Clients ask both as one question - "can we still change the number?" - and get an answer about whichever case the person on the telephone had in mind. Say what happens in each direction, separately, and say what the ceiling actually is.

The timestamp is the whole dispute

When a venue and a client disagree about the count, they are almost never disagreeing about the number. They are disagreeing about when it was last given and whether it was acknowledged. A count said aloud at a tasting, mentioned in a reply to an unrelated e-mail, or texted to a coordinator's personal phone has no timestamp anyone can produce later. A logged change request has one, and that is most of what it is for.

What must still reach a person

Whether a specific increase fits the room, whether the kitchen can absorb it this close in, and what it costs are decisions with money and safety attached - they belong to the coordinator. The useful division of labour is that the published deadlines, the direction-specific rules and the request log are handled automatically at eleven at night, and the judgement arrives with the coordinator in the morning already written down.