How does Year-End Journals know an invoice covers a period?

Each invoice line's wording is tested against families of patterns — a date range ('1 Jan to 31 Dec'), a named quarter ('quarter to 31 March'), a month, a 'year ended' phrase — in an order that keeps a quarter from being mistaken for its last month. A line no pattern fits is offered to AI only when the AI fallback is on, and the proposal says which read it, with a confidence. The split is straight-line by days: days after the year end on a purchase invoice are a prepayment, days before on an unseen bill an accrual; on sales invoices the mirror is deferred or accrued income.