I recently bought a used Nikon 12-24mm 1:4 G ED lens in almost mint condition. My camera is a Nikon D5100.
I compared it to the similar spec Tokina 12-24mm by looking at a lot of different reviews online.
After taking a few shots with my acquisition (and being pleased with the results), when I look at the 'Info' section on my Apple PC (downloading to iPhoto), it shows as if the photos were taken by the very Tokina lens that I was comparing it to. This does not happen with any other lens I have. They show the correct description.
Any ideas? I think I either have a copy of a Nikon, or else my PC knows I have been looking up the Tokina 12-24 and has got confused. There is nothing on the lens to suggest it is a copy.