You can show this easily enough by looking up older datasheets. For example the Intel 8255*. It had two 8-bit ports and a third which could be split into two four-bit ports as control lines for the other two ports. Its datasheet would have been published way back in the early 70s. In its table 1 you will see the control ports described as upper and lower nibbles (not nybbles) of Port C.
* the PPI chip at the heart of most of the DIO cards I used back in the early 80s for the brief period I actually practiced as an electronic engineer before switching to aviation