Qr Code Questions

I am SO thankful for these QR codes; they are making my life so easy with Santa photos this year! Having 0 clues about how the technical coding of these works though, I have a list of questions.

1. When I generate QR codes without subject info for a gallery, are those codes then linked to that gallery? Or if they are unused for that gallery can I use the printed code for a different job? 

1a. If I generate codes for a gallery and then later create sub-galleries, will the QR codes and passcodes still work for images in the sub-gallery? Or do I need to keep everything within that main gallery?

2. If a QR code is unused, is there a way to expire it? Or do they expire after a certain amount of time so the code can go back into rotation? 

3. Is there a chance of a QR code being generated more than once? (Either by myself or by me and another user.)

4. When I use QR codes with associated subject data, I can see a list of the codes/subjects in the gallery. 
When doing a public event where I don't know the subject info ahead of time and am just loading codes and photos, is there a way to see a clickable list of the codes and associated photos after they are loaded? (Not the verify QR area. Something similar to what we see when adding subject info.) 

Thank you! 

1) The QR codes aren't really linked to a gallery. When the code is entered or scanned, it will find the photo with that code and direct to the gallery it is in. 

2) QR codes without subject info aren't saved in the system. So if one is not used, then it just doesn't exist. 

3) When a QR code is generated it checks twice that it is unique so unlikely one would duplicate.

4) There is not a list of codes in that situation. You will see them under the thumnails in the gallery in the admin. 

If 4 is important to you, then why don't you create your own random data in a spreadhseet ahead of time, and import that from a .csv?