The part no template page will tell you, because it only shows up in service. Each of these is a documented failure, not a best practice.
The guest count only moves one way
The guaranteed count is a floor, not an estimate. It locks a few days out: anywhere between 72 hours and five working days, depending on the venue. After that it can only go up. Everything is bought, staffed and costed from it. If fewer guests turn up, the client still pays the guaranteed number. If more do, the difference is billed. And that number rarely matches the room. Of the guests who accepted, 5 to 10% do not come. On 150 confirmed, that is 8 to 15 seats you have already paid for.
Vendor meals are a second count, with no deadline
Vendor meals do not count towards the guest number. That is a trade convention. The DJ, the photographer and the videographer still eat. They are simply not seated with the guests, and their meals are billed separately. So two numbers sit on the same sheet, and only one has a deadline. The kitchen finds out about the second on the day.
A quarter of an hour lost on the steps
The classic "11am at the town hall, lunch at 1pm" plan does not hold. Congratulations alone run about an hour per 100 guests. The drinks reception gets crushed: neither a real pause, nor a real start to the meal. A Paris caterer proposes this run instead: ceremony 11:00, photos 11:40-12:10, drinks 12:45, lunch 13:30. Those 30 to 45 minutes are the whole difference between a service that works and one that runs. A quarter of an hour lost on the steps is enough to undo it.
Speeches are not on the programme
Toasts go between courses. That is the convention, and that is where unplanned ones get expensive. Three speeches slipped in between the main and the dessert, when the kitchen has already plated: the dessert goes out far too early, or it waits under a pass lamp. A corporate event does not do this to you. Its interventions are on the run sheet.
The cake does not behave like the rest of the meal
Many pastry shops will not deliver. The cake arrives in a private car, with no slot and no named contact. It cannot go in the fridge: humidity attacks caramel and sugar paste, and weakens the structure. It needs cool and dry. That category exists on no template. It is also assembled on site. A cake delivered at 1am and served at 2:30am has already been reported. So it needs reserved space and reserved time. Neither is ever written down.
Some information is carried by a person, not a document
A head waiter verbally agreed that a couple could leave their decoration in the room overnight. Then he left the company. The week of the wedding, management said no. The couple cleared the room the same night, with family and friends. The information existed. It was on no sheet. This is exactly what a BEO is meant to prevent, and exactly where it most often fails.
Allergies: the last link is a handwritten seating plan
The sheet says "2 gluten-free". It does not say which chair. The last link is a table plan drawn up by the couple, often the night before, for people who will move seats during the evening. And the last person informed is the commis carrying the plate.