Good tip….. Been given before by CC members.. Don’t think this has changed.
When booking flights with Cunard, one is only allowed to book seats as/when cruise balance, plus flights, are paid for (cruise balance due date) as it is only then, when the flight locator reference given, this to enable seats to be booked.
By then, it is possible all decent seats have been taken.
Best to pay for the flight when booked, then (think) 11 months from flight date, when the flight opens, one receives the flight locator, then immediately go to the carrier’s site to select/book seats.