12/5/19 Identification procedure has been updated
To the Users of the EF300mm f/2.8L IS II USM, EF400mm f/2.8L IS II USM, EF500mm f/4L IS II USM, and EF600mm f/4L IS II USM Interchangeable Lenses for Canon Digital SLR Cameras
Please see the changes to the “Identification Procedure” section below regarding the criteria for affected serial numbers. The identification procedure has been enhanced to include the first, second and third digits from the left in order to more precisely identify affected products.
Thank you for using Canon products.