Pin Connector 62462 vs 75535
I have seen one possible explanation posted in a comment in this question:
Why does the pin recess on the Technic turntable continue to the edge of the part?

User Joubarc states:


  Another good (if maybe more subtle) example of this is the pin joiner
  which now has a slot in the middle. That slot is similar to the recess
  seen in the other parts, in that it simplifies the moulding process
  greatly. (The previous version required two sub-parts to be assembled
  together, which is even worse than a mould with moving parts)


If this assertion is true, then the slot exists simply to streamline the molding process. If you look closely at the top-rim of 75535 in your example image, it is easy to make out a very fine line. Perhaps this is evidence of two sub-parts being assembled.