The title is a misnomer.
The titular "androids" of Andre Norton's Android at Arms
aren't. Nor are they the originals they start out thinking they are. They are actually clones
created by the mysterious operators of their prison planet, who accidentally rediscovered a science so long forgotten (and forbidden?) that even the name for it had been lost. Realistically, there is no other way that both Andas Kastor and the older ruling self he finds in power when he gets back to Inyanga can both be - as they quite explicitly are - fully human.
- Part of the problem here is in the definition of "android." As The Other Wiki puts it, "Authors have used the term android in more diverse ways than robot or cyborg. In some fictional works, the difference between a robot and android is only their appearance, with androids being made to look like humans on the outside but with robot-like internal mechanics. In other stories, authors have used the word 'android' to mean a wholly organic, yet artificial, creation. Other fictional depictions of androids fall somewhere in between." (I added the italics.) So it could be the android makers used cloning ... or something else that produced a similar result. There was a book I read in which someone, as an experiment, created two men, one eugenically bred and one "synthesized," but identical in appearance and both equally capable of functioning as human beings.