Function uk_latest_rpi 

fn uk_latest_rpi<C: InflationCurve<f64> + ?Sized>(
    bond: &InflationLinkedBond,
    settlement: NaiveDate,
    fixings: &FixingsView<'_, f64>,
    curve: &C,
) -> Result<(f64, NaiveDate), CurveError>

The latest published monthly index print strictly before settlement’s month, scanning back up to eighteen months of fixings and falling back to the curve at the previous month start.