Was the option that was altered developed specifically to handle the impact of the terrorist attacks?
No. This option is used as a part of standard seasonal adjustment procedures at the Census Bureau but with a more conservative (restrictive) definition of what constitutes an untypical month. For these months, a definition of untypical was used that is customary in statistical practice when there is advance knowledge that the month's survey value has a strong potential to be untypical.
For more information, visit the Monthly and Annual Retail Trade website.