PocketBook 626 Touch Lux 3

Hi there. I'm trying to buy used Touch Lux 3 and I can't understand something. Some of the books have on theirs back side sign Touch Lux 3 and some of them don't. Sellers gave me proof that this is the same book but I'm still hesitate. Can someone explain me what the difference? Why do some books have this sign and others don't? Some kind of different revision of the books or they just trying to fool me?
Thanks in advance.