You may consider Thru hiking whatever you want, for yourself but as for the ATC, try again. Straight from the ATC website:
Thru Hiking
A thru-hiker is a hiker or backpacker who has completed or is attempting to walk the entire Appalachian Trail in a 12-month period (not necessarily a calendar year).
I found this in 30 seconds, after remembering reading it during my research.
Sorry, but people who publish wrong information need to be corrected.