The index data is frozen with a four-quarter lag.
Due to the inherent lag in financial reporting, financial statement data is not published until up to four quarters after the financial year end. For the purpose of the index computation, any gap is filled by extrapolating the financial statement data to the index as-of date. Consequently, the index results for the last four quarters are indicative only. On the other hand, results for dates more than four quarters before the as-of date are based on realised financial statement data and are thus frozen.
Things to consider
In practice, this has been since inception achieved by computing indices from scratch every quarter. The published indices are updated by merging previously frozen output with the output from the new computation.