Wow, Great pictures Larry, as you point out the seam lines are one of the keys.
Patterns are used to replicate each piece time and time again, if you were to build multiples of something (Kirkhams) you would definitely replicate steps, hence patterns, templates, software
Quality control and cost!
The removable pedal box was introduced (Kirkham, 427) somewhere between car 45 and I am guessing 100.