An event in the books
Deposits held as client money, every cost tagged to the event, and a margin read when the last bill is in.
Booked in March, deposited in April, held in November, billed the next morning, the florist's bill in December. Whether the wedding made money is a question the books can now answer, because the event is a ledger of its own — deposits held as client money until the event, every vendor bill line taggable to it, the margin read when the last bill arrives. The accounting page on the banquet ledger says how.