Head Scratcher #3: Gene-seed

A relatively straightforward head scratcher: what's up with how gene-seed is handled?

According to the old white Dwarf Articles on rites of initiation, there are two progenoids implanted as part of the gene-forging process; one in the neck, one deep in the body. After five years, the neck gland is mature and ready for removal. After ten years, the body gland is mature and ready for removal. The glands may be removed at any time after maturation. That's what it says right there in the article.

Now the question: why the flippin' hell does a Chapter wait until after the Astartes is dead to get his gene-seed? It's right there in the article, and as far as I am aware, it has not been retconned or changed in any way - although, it has been a long time. I have heard some explanations that the progenoid performs some sort of regulatory function so it is left alone until the point of death, but I have not seen any concrete, canonical reference to that effect. Now to be fair I don't own the entire Black Library's suite of novels, but I am slowly working through them. If anyone reading this can provide a concrete, canonical, irrefutable reference that explains why progenoids are left in until death, please send it to me so I can put myself at ease.

Another explanation I've heard is that the progenoid deep in the body cannot be removed without killing the Astartes, and I think I've seen that once or twice in a novel; but again, the original article is very clear and unambiguous.

The reason why I ask is because gene-seed is so important to a Chapter for so many reasons; it is their link to their Emperor and Primarch, it is what makes an Astartes what he is. It is a form of immortality; even though he may die, some part of him lives on through the gene-seed he donates to the next generation of the Emperor's finest. So then why the hell is gene-seed risked so recklessly?

• Plasma and melta weapons completely vaporize and melt; no more gene-seed for you! Even a very lucky bullet or bolt shot may destroy the progenoid organ.
• Excessive exposure to warp energy or radiation may mutate gene-seed and render it useless.
• Tyranids and kinds of nasty gribblies may try to eat Astartes, and the gene-seed along with it.

And that's just off the top of my head. If I were an Astartes (and I'm not, but if I were...), I would have my progenoids removed as soon as possible. Period.

1/17/12 Something else that occurred to me. If a scout is halfway implanted and then dies, what happens to that gene-seed? Can the Apothecaries just, uh... take the organs out? And then put it in someone else? Because, if a scout is halfway implanted and then dies, and then those organs are not usable, then the other half of unimplanted organs might as well be worthless since they are just extras. Or, can you take organs from one progenoid, the rest of the necessary organs from another progenoid, and then just combine them together?