I have come across a website that provides day-to-day readings of atmospheric pressure & oxygen concentration levels at a number of altitudes. One time I observed that the oxygen levels at K2’s summit are a tas bit lower than they were on Everests summit...(Part 1)

Such readings indicate that the altitude tagged as the lower limit of the death zone (8,000m) is not fixed, but fluctuant. Thus, altitudes slightly lower than 8,000m (eg: 7,800m) would occasionally experience lower oxygen concentration and atmospheric pressure levels. (Part 2)

Such natural occurances would temporarily include high 7000’ers as peaks that fall withing the death zone, and exclude low 8000’ers such as Shishapangma from the death zone peaks list.