These distinctions are imported from Chinese, where 叔母 and 伯母 are pronounced differently, although nowadays 婶婶 is much more common than 叔母 and both only refer to the wife of the father's younger brother, while 伯母 is an older brother's wife.
There are many more different terms for various fine distinctions of relatedness, but I only know those I had a need to use, and when I asked a Chinese friend for help, he told me that he can't remember all of them either.
There are many more different terms for various fine distinctions of relatedness, but I only know those I had a need to use, and when I asked a Chinese friend for help, he told me that he can't remember all of them either.