I looked at your thread and it's pictures in your post #146 where the splines on your shaft are perfect.

can't comment about why something like this didn't happen to you, but this instance could be due to someone being in that tranny previously or it could be something as simple as poor quality control somewhere in the supply chain or the assembly line.

My point was it's obvious that there is extreme wear on both the shaft and the yoke, extremely unlikely that would have occurred over a short time to end up looking like it does.