Interesting find, I will have to think further on this. As this sometimes seems to go, you begin to wonder how much more you can check.
For your last question: below is a diagram for the driver seat. I assume you are referencing the #5 part? This is the K40D - seat memory control module. This module has 5 connectors (X1, X2, X3, X5, and X6). So it sounds like there is presumably an X4 connector that is not there by design.