Unfortunately, though interesting in the details the"reasons" given as to why Iodine disappears are not exactly accurate.
Iodine disappears on any surface exposed to air because of oxidation. The variant as to how long that takes has more to do with the temperature and humidity etc. of the external environment to which the painted area is exposed ( i.e. if one spills some on a counter top it will eventually disappear even though it is a mess for a day or so)than any real indicator as to what the body is using or not using.
Another tale from the crypt I am afraid.