Why are there different 727 and A833 slip yoke lengths???????

I have been looking for a 29 spline 7260 yoke. I have noticed there are different length factory slip yokes. I have noticed that some of the length difference is where the splines start inside the yoke. Some splines start a little deeper than others or their is just extra material before the splines start. The yoke I have is 8" and others are 9" from center of yoke to slip end. Can someone shed some light on this?