aramis erak
Legend
It is away to write a rule.
The fact different people can interpret the same text in diametrically opposing ways should be seen as a major failure, not as something positive :-(
pretty much every rule that exceeds a simple sentence can be interpreted multiple ways.
I'd interpret "not less than 16" to mean it only raises AC if your AC, counting all other sources, was less than 16; nothing stacks with it, but at the same time, anything that stacks with your worn AC continues to do so. In other words, Barkskin's useless on a guy in plate, unless he has a penalty from a curse or other special case.