This is a term that I coined in 2001
Presumed Public Knowledge is the information that people presume to be true and accurate because it is commonly purported by the general public. Sadly, it is often not true or accurate information; but people rely on it as if it were carved in stone.
The origin of Presumed Public Knowledge is generally from Religion, but also includes Traditions, Superstitions, Wives Tales, Folklore, etc.