This is my daughter’s theory for locking the passenger side only.
"Guy opens the passenger door for girl, girl slides over and opens the driver side door while driver walks around to get in." Just good manners, makes as much sense to me as any of the other hair-brained guesses.
How you coming on that truck Jordan? Got your license yet? We haven't been hearing to much lately, hope your not running out of steam. That's what happened to me back around 1956 or 1957 with a '34 Studebaker coupe. I sold it to buy something that ran when I got my license and to this day I regret not keeping it.
Denny Graham
Sandwich, IL