So hard to say, I've gotten some "replacement" ribbons in packages that I SWEAR were real MLP ribbons but the person told me they went out and bought them at the store, so... I'd personally stick with your middle ones as a guideline, and maybe keep your others in a baggie set aside until you can truly figure out if they're real?
I have a HUGE pile of authentic ribbons that I need to organize, but they're all the same size, and many of them carry much fading in them... whenever I see a really bright ribbon I hesitate just a bit because of all the other ones I've owned have definitely been "lighter"...
hope that helps a little, lol.