The difference between address A and address A+1 is one byte. By definition.
Some hardware may raise an exception if you attempt to retrieve a value at an address that is not a (greater than 1) multiple of a byte, but that has no bearing on the definition of a byte.
Some hardware may raise an exception if you attempt to retrieve a value at an address that is not a (greater than 1) multiple of a byte, but that has no bearing on the definition of a byte.