This is the age old question. The answer is very simple, but seems to be a concept that most people canít grasp. A variation is an INTENTIONAL change like in the Saga line - Kit Fisto sticker change, Anakin Hanger blister change, figures that came w/BG then w/o.
An error is just that Ė a MISTAKE. It was never meant to happen and is usually one of only a handful. Like a figure missing a weapon or with the wrong accessory or even NO accessory. Like the Dooku with unpainted cape chain, Yoda missing his lightsaber, etc.
The other thing is a Hoax - any item that is only sealed by tape - it can be opened and resealed. 12 inch, vehicles, cinema scenes, 300th Fett, etc.