To a point you are right to wonder. But when you are talking about many centuries, it would be far more time-wasting to say many hundred years, or in saying one hundred and fifty years instead of a century and a half. The word century comes from Latin cent meaning �one hundred� with �ury� loosely turning it into �consecutive years�. So in some respects it is why some people say the 1400�s or the 15th C (early or late). It defines an era either way.
Prior to the 18th Century (or 1700�s) though, �hundred� could mean anything up to 120, depending whether it was a small, long or great hundred. This all comes down to the evolution of Centum-Satem, so embrace our modern language.
Apparently � it may be a myth � but I have heard that the Japanese have over a hundred words for the word �early�.