Ok so no matter of your opinion of Fear to Tread be it good or bad the book has shed some light on the numbers, organization and workings of the IX legion at the time of the great crusade.
i) Legion of approximately 120.000 astartes.
2) Legion divided into 300 companies each with its own captain and hierarchy.
Now this leads to some interesting questions, usually a marine company during the heresy era is given as 1.000 marines, the equivalent of a 40k chapter, however simple math tells us this cannot be the case as if that was the case the legion would be in the 300k+ margins.
Furthermore is the issue of how the apothecarium, legion chaplains ( wardens) and techmarines are structured. Do they exist in their own companies and then seconded to the rest, exist outside the normal legion organizational template or are impeded and exist at a company level. A case can be made for each of the above.
I would like to hear people thoughts on this matter.
Personally i see it as the following, BA companies consist of approximately 500 marines at full strength. techmarines, apothecarys and chaplains (wardens) exist outside of the normal legion organization and are seconded to companies as required.
The 120k mark is of battle-line astartes and does not include the like of scours, chaplains ( wardens), sanguinary guard and so on, very much as the 40k chapter organization functions.