It sounds good so far
I would add more but I am having trouble picturing this "cyborg". If he is just a guy with an artificial limb the laws should reflect that, he has human?-DNA but no records and some form of amnesia then why is he by default not considered human/a citizen/whatever. If laws were not in place to do so then unscrupulous people would make it a habit to falsify records to enslave people (or whatever the creator has rights to do to their created).
It would kind of be interesting if the sign for a biological creation was a genetic signature (string of chemicals written into the DNA especially if they are not themselves DNA)registered at some facility. so all our hypothetical antagonist have to do is register for a signature then release some sort of retrovirus to tag whoever they wanted to claim as their creation. So how do the courts decide if it is challenged. If you think about it long enough you should come up with a interesting story. For Example, the lawyers argue that since the being in question is older than the application for signature the counter is that the being just looks that old etc. Needs documents, Fake Documents, etc, etc.
It might be easier or harder on your character if he doesn't look human. such as a brain in a jar or a human with a obvious artificial skin/exoskeleton. on the one hand looking human means that people will sympathize with him, but it also means that he is less likely to have fallen through the cracks accidentally like in your post. ie where is his family, where is his genetic donor if not the model they originated him from if made from scratch. On the other hand if he looks like a brain in the jar, It would behove a technologically advanced society to test his human-ness does he have human?-brain cells, etc.
More to the point have you planned out whether or not his creator is alive, etc. even if your story does not go out that far that character will drastically influence the story.