Flute lower bound lower than most people say

[caters]

Most people and sites say that the lower bound for the concert flute is middle C. However I have seen pieces that require you to go even lower. I have also heard that the lower bound for the concert flute is actually A in the small octave.

So if the concert flute can go down to A in the small octave than why do most people say that the lower bound is middle C?