I just read through large parts of a master's thesis by Samantha Ackerley called "
Preserving Jeff Wall" - all about his lightbox transparencies and their deterioration. The program Wall refers to is to create a supply of transparencies that can be used to provide replacements for the ones in existing lightboxes when the time comes to do so. A transparency (printed on Ilfochrome or Fujitrans) is only expected to survive up to 12 years. Apparently, at the time of that thesis (2014), his
Destroyed Room lightbox still contained the original transparencies, in spite of being the most displayed of all lightboxes.
Some interesting ideas about what constitutes an "original" artwork are briefly mentioned in there, since the lightboxes themselves have undergone modification over time that actually has some impact on the final appearance or experience of the art. So, it's more than just these lightboxes no longer contain the actual photographic element that was originally in them, but the lighting elements have been altered which changes the temperature or brightness of the colours. The main interesting idea is, if the "original" is whatever the source is (a film transparency or a digital file, in the case of digitally produced images), then what is it that the galleries are buying?
Wall maintains complete control over his artwork, including the rights to determine if and when a transparency should be replaced and also whether or not a work should be withheld from public display.