As an army helicopter repairman in 1956-1958, I was taught that a splice or termination is never soldered because the stresses of the extreme vibration in a helicopter would concentrate at the transition zone between the rigid, soldered wire and the unsoldered wire leading to the possibility of an eventual wire break at that point. As a now retired 40-year noise and vibration engineer, that analysis still makes sense to me. You want the bending due to vibration or repeated handling to be distributed over as long a section of wire as feasible to minimize fatigue at the focal point of bending.

Looking at the figures in the NASA document, I can see that the soldered splice of figures 19-8 and -9 could provide good fatigue resistance PROVIDED the parallel wires were bound together with tape or shrink tubing (not shown, and shrink tubing didn't exist in 1958), so that the stress of vibration or repeated bending would be distributed over a length of unsoldered wire, but the splice shown in figures 19-10 and -11 would concentrate stress at the soldered transition zone despite the minimal support offered by the shrink tubing.

And, except for a temporary emergency repair, why would you ever allow a splice in the middle of a wire run at all?