4/6/7 pin S-video cables?!?! are all s-video inputs capable of accepting any amt of pins?

im looking to order an s-video-to-RCA adapter and online they sell them by 4 pin svideo, 6 pin svideo, 7 etc. ! why? ive never heard of that in my life! isnt s-video a standard out/input cable? Perhaps ALL inputs have the full 7 sockets and if you have a 4 pin cable the other pins just remain empty? or do i have to figure out which one i need? ive purchased s-video cables multiple times and never had to match pins before.