Traditionally the patches were never added to the Reebok jerseys of late, so they make it easy to spot a fake. They have started putting the AFL 50th patch onto the throwback jerseys, so i don't know if this is going to continue or not. I would think that they add the patches to anni jerseys as they aren't team specific and can be made in high numbers keeping the cost down.
Individual team anniversary patches would be more of a pain for Reebok as it's only for one season and would be in small numbers, that's why they haven't released an official Captains badge to the public or put the superbowl patches on, too much work for little gain. A lot of people buy the Willabee and Ward patches and add them themselves.
The 75th Anniversary patches are real if it's on a vintage jersey. I've seen some real rotters on fake M&N jerseys.