Board Thread:Warhammer 40k General Discussion/@comment-64.121.236.162-20140910042956/@comment-8881468-20140915074042

to me it does not matter that much wether they cared about replenishing their ranks.

creating a space marines takes several years, so during the heresy they would not have had that much time to counter their losses

add in the problem of replacing the kills of the loyalist legion parts and other methods, leading to loss of gene-seed, regardless of how big their stockpiles were, they would all have been more than hard pressed to replace 50% or more of their legions

which is only complicated by the tainted or dead primarchs and no access to pure gene-ssed templates.

as far as replenishing their ranks after the heresy: if you remember "deliverance lost", both the alpha legion and the sons of horus had access to the primarch project data and findings and on terra there was even more data on the primarch and space marine research....

also the dark mechancum would actually allow innovation and research, which in turn can lead to the space marine project or other soldiers.