[Tedathalan]

Thanks for the responses. So in general, failure rates should be extremely low, given the screening aspirants go through.

However, if the implants begin being added, and they fail, it essentially means that a full set is wasted, yes? The implantation process takes years, and if the process fails at any point, it's not like they can just give the remainder to another recruit.

I know progenoids are the last to be implanted, but I'm assuming they won't work unless the process in general is successful.

So in the Blood Angels example above, two full sets of organs are harvested from a dead Marine's progenoids. They are implanted into aspirants, many of whom don't survive the process. Regardless of the stage at which they fail, the un-implanted progenoids (proto-progenoids?) can't be saved for anyone else, since each potential marine's body can only support two, yes? Same for any other organs that have yet to be implanted, so a begun-but-failed transformation is essentially a waste of half a Marine's contributions to the chapter.