1st gen iPod nano's not involved in replacement program

I recently looked to send my 1st gen iPod nano (purchased within the time frame stated) off as part of the replacement scheme due to the battery defect found in this model

After entering the serial number on the back a message appeared telling me my iPod could not be replaced.

I am certain I purchased the device within the allotted time frame eligible for the program and ask:

What criteria, after purchase date, determine whether or not your iPod is valid for the program, and why my iPod could possibly not be?