cam gears

Hello, I have a set of barely used Comptech /CT-Engineering cam gears for sale. They are in great, working shape, with the only noticeable wear being the paint wear to one gear that rubbed against the plastic cover. From the manufacturer: "Adjusting the cam timing is the key to unlocking...

Need help from the experts. Looking at cam gears and saw a couple aside from the well-prescribed comptech ones. I saw AEM and TODA has them but what i don't understand is this; Why do they both sell cam gears as FR EX/ RR IN, RR EX, FR IN. When you buy them, don;t they normally sell 4 pcs...