Legion Military strengths after the siege of Terra

[Legatus]

The fluff suggests both, and certainly declares neither to be definitive. I'm only saying which one makes the most sense. You're just arguing simple to be contrarian at this point, lol.

Ah, I see. It seems I simply have more information.

"A Space Marine begins his training when he is little more than a boy. At the same time a series of genetically tailored organs are carefully implanted into his body. (...)

Organ implantation goes hand-in-hand with a harsh routine of physical and spiritual training. This is achieved by means of hypnotic suggestion, prolonged meditation, vigorous spiritual tests, and gradual initiation into the cult rites of the Chapter."

(2nd Edition Codex Imperialis, p. 18)

"Those youths who are accepted as Aspirants are taken to the Blood Angels' fortress monastery on Baal itself. There they see great wonders and look for the first time on the unmasked faces of their future Brother Marines (...)

All the Aspirants are left to observe the vigil in the great Chapel of the Chapter and then they will drink from the Sanguinary Chalice brough to them by the Sanguinary Priests. They are told that they partake of the blood of their Primarch and they drink. Slowly slumber overtakes them and they are borne by Servitors to the Apothecarion where the gene-seed of Sanguinius will be implanted in their recumberent bodies."

(2nd Edition Codex Angels of Death, p. 19)

"Every Chapter of Space Marines must recruit new warrior into its ranks in order to survive. The Dark Angels select these so-called aspirants from a host of worlds, over which the Rock orbits while the rites of selection are performed below. (...) Warriors must always be chosen when they are still young, before their bodies become too mature to accept the gene-seed which will turn them into Space Marines. This procedure of implantation is just the beginning, for it takes several years for the genetic implants to turn an ordinary Human into a full Space Marine."

(4th Edition Codex Dark Angels, p. 18)

I thought it was a given that the Aspirants are being prepared almost immediately after being selected ("immediately" as in "withing a few weeks of being selected"). Granted, most sources do say that the Aspirants are "tested" before the implantation process begins, but assuming that that testing rpocess takes several years is quite a stretch, and not really supported anywhere. Quite on the contrary, as the examples form above show.

Or maybe you believe that the Blood Angels have an exceptionally short testing time? Would you believe the same of the Dark Angels (who are said to be quite thorough in their testing)? Their description stresses that the Aspirants have to be picked before being too old for the implants. Not "several years before being too old for the implants". The description also mentions how the implantation process takes several years. If the prior testing process would also take several years, this would have been the spot to mention that.

[Raven Angel]

Page 8 of the 1st Index Astartes contains a chart list the ages at which the implants are given. According to this age 10 is the youngest a child can begin the transformation and age 12 is the oldest he can be. The process takes 6 to 8 years to complete with the age of 18 being the oldest that the last 2 organs, the progeniods and black carapace can be implanted. Also it is posible to make SM out of older people but it is not done any more. The verious excelerated technices where in part blamed for the corruption of the traitor legions and the use of this technology forbiden after the HH. The cut off age is not mention but I assume it to be in the 30s or early 40s as Luther of DA legion was not actally a SM but an enhanced human. he was too old. Also the 2nd of the DA HH books says they where cranking out new marines in less the 2 years.

[Conn Eremon]

I think there's also the possibility for some (several? dozen? hundred?) Chapters being founded with a few hundred Marines, and it being a case of "Now start recruiting."

 

This is precisely the manner in which I've always thought of it.