The National Classification Management Society in conjunction with the Defense Security Services published a guide for preparation and issues pertaining to the DD254. The guide can be located at http://www.dm.usda.gov/infosec/DD254.pdf
. My understanding of the guidance is that when there is a change in classification guidance, a revision can be issued. The text from the guide dealing with revisions is below:
When there is a change to classification guidance, a Revised DD 254 is issued. Give a sequential number to each revision and enter the date of the Revised DD 254.
• Enter the date of the Original DD 254 in 3a.