Four values, three calculations
Assume an invented index actual of 102.4 and a private calendar forecast of 102.1. The previous period was initially reported as 101.8 and is now revised to 102.0. These numbers are instructional, not a real release.
Actual minus forecast is 0.3 index points. The previous-period revision is 0.2 index points. Actual minus revised previous value is 0.4 index points. Using the old 101.8 instead produces 0.6. Always identify the version used. An index-point change is not automatically a percentage-point change.
Forecasts need their own provenance
Store the official release URL separately from the private forecast provider, capture time and units. A market expectation collected by another organisation is not an official BLS forecast.
Preserve the information available at the time
BLS explains that additional information and statistical procedures can lead to revisions. Retain the originally observed release alongside later revised values. Replacing a historical observation with the current value changes what the observer could have known then.
Connect the release record to a price observation
Record release date, reference period, time zone and source. Set price-observation times separately. A price move close to a release does not by itself prove causation. Put simultaneous news, liquidity and possible data delay into the unresolved-conditions field of the journal.