In the KFMB video about Netflix, I noticed they made an error in the reporting. The reporter says that the machine that process 17,000 pieces per hour is "stamping" the envelopes, but that can't be, because the envelopes are all pre-printed with a prepaid permit.
The video also mentions some machines which were kept secret, and not permitted to be videotaped. I think I know what those machines do. They scan the envelopes through the little slot in the back which reveals the disc's barcode. Once the machine knows which title is inside, it knows which subscriber to send it to, and prints the name and address on the envelope.
Regarding "notes to Netflix": If you watched the video closely, you saw how quickly those people were processing the discs. Do you think it's possible they would even notice a note, or want to read it? If they are paid per piece, on a production basis, then a note on the sleeve would be an unwelcome obstacle.
What do you think?