That means it was a closed, proprietary system that was reverse engineered & emulated. Different from an open system that doesn't require that. Also more efficient in hardware if any clones port original design.
Did they give you copyright and patent licenses allowing you to do whatever you wanted with their tech? Or did a cloner have to hope the company would take no legal action?
Because that's still not equal to an open-source design where the licensing eliminates such risks.
C64: http://www.classiccmp.org/cini/pdf/Commodore/C64%20Programme...
C128: http://www.pagetable.com/docs/Commodore%20128%20Programmer's...