The Key of Changes shows the 8-digit AHECC codes that have been replaced or added to the classification. It is a historical concordance between old and new codes. The attached Acrobat file contains a listing of all changes to AHECC codes that have occurred since the original version of the classification (produced on 1 January 1988) including changes introduced up till 1 January 2006.
The list has four columns:
|Previous code||The code that has closed|
|Replacement code||The new code(s) that replaced a previous (or closed) code.|
|Date replaced||The date a previous (or closed) code ceased to operate, and was replaced by its new code(s).|
|Expiry date||The date a replacement code operated until, before it was replaced by a new code.|