REcalling when I worked behind a camera counter, I can see things like the "return Negatives in the Cassette" as being a great way to protect the consumer from Him or Her self. I have had to avoid cringing when someone came to the counter clutching their negative between thumb and forefinger, and inquiring about an enlargement.
To offer that one feature the Lab had to have a machine to detach the film from the spool, another to trim the end of the film, and a machine to spool the Processed negatives back into the cassette. Unless you knew the trick, the negatives were impossible to extract in the consumers hands. I suspect that the desire to maintain that feature was responsible for the lack of enthusiasm for home developing equipment.
Like Disk - the twin-check was no needed as the film package and the film itself had a unique number. SO high volume labs could probably just feed order envelopes into the process and have the film number printed on the envelope, when the cartridge was fed into the processor. Likewise, the developed cartridge likly could be fed into the Higher end printer and the order prepared automatically.
the print would have the film number and teh exposure printed on the back, so no one had to look at (or Touch) the negative to order reprints. (also like DISC)