Your fender has the lower brace that goes from the fork leg to the rear bottom of the fender. The /7 does not have this bottom brace. The /6 fender is longer than the /7 fender. It provides more protection in the back and keeps a little bit more dirt or mud off the front of the engine. They are popular with some riders because of this. But there are other differences and if the brace at the top of the fork sliders is a /7 this fender doesn't fit correctly there with out removing some material.
It's not a big deal unless the bike is entered into some competition. A collector will notice it if they are looking for it.
Never memorize something you can look up.