I had the good fortune of touring Kodak's Palo Alto Lab in the early 1980s, and was amazed at the processes involved in processing both slide film and print film. Even then, it was conducted by computerized equipment that adjusted exposures during processing. Still remains one of the most significatn "tours" I ever had the opportunity to make.

As for mailing in films, I recall there were only two Kodak labs remaining in the 1980s: Palo Alto, and Rochester, NY. All films turned into, e.g., Longs, or Walgreen's requesting "Kodak Processing," were sent to one of these two labs. Also, the consumer could deal directly with the Kodak Lab by purchasing Kodak Mailers. Film would be processed at the lab and returned by U. S. Mail. It was a real shock when the Palo Alto Lab closed down, and all processing was shifted to Rochester. Prior to that move, the PA Lab operated two shifts to keep up with the demand.