This spreadsheet is updated quarterly. The spreadsheet always contains data for 40 rolling years. Each new release removes the oldest data and adds the latest available data. In addition, previously published estimates may be revised for the following reasons:

1. Estimates based upon provisional data are revised when final data becomes available.

2. Revisions may also be made when methods or systems are improved.

These types of planned revisions should not be confused with errors in released statistics, which are genuine mistakes. Such mistakes occur rarely and, when they do happen, corrections are made in a timely manner, announced and clearly explained to users in line with the Code of Practice for Statistics (Quality pillar, practice Q3.4).