~~~ which was thought to be damage causes by sunlight or artificial lighting was actually explained to us by someone in the offset business as being an oversight in the printing of the litho inlays of Paulson chips during a run of Resorts Int'l chips where the coated stock was a beige/rust color between dark and light and that somehow was part of the production. It's xplained here a lot better than I did by that person and was really quite imteresting... Some of that run had the dark inlays on one side and both sides.

The sun and lighting can also cause that effect but, the difference was pointed out in several posts compared with no discoloration on the Paulsom chips with the dark inlays.