Is it necessary to recalculate all time series when new data become available each year?
Yes. Adding data of a new year may lead to changes in the computed indices of previous years. Indices are based on a statistical model for the entire time series and adding new data to the model may affect the estimated parameters for all years. That´s why new indices for all years are calculated each year. Usually, however, changes in indices of earlier years are small and within the confidence intervals calculated in earlier runs.