Why is it that if you look at photos of fords N R S K 09 no two of them seem to have the same horn. I have owned most of the horns and I'm a bit confused as to the variation. All the horns are Nonpareil or Rubes but some have large bells, some have small bells, some have the door on the outside, and some have the door that joins with the bell. Was it just a "pick what you like" or was there a method to what horn went on what car?
I do not doubt that originals were commonly replaced at some time in the life of the car. In addition to crunch damages, the early jobs with the bell facing up tended to collect water, where I assume this could either rot out the tubing and/or possible freeze in winter weather. I also doubt auto manufacturers were really concerned about running production changes to functional parts like this. The horn had to operate, stay mounted, and look presentable. My guess is that Ford sourced these parts from multiple suppliers who met these basic criteria.