Board Thread:Warhammer 40k General Discussion/@comment-64.121.236.162-20140910042956/@comment-8881468-20140911072201

yup but those 7 years saw them kill a load of their own (and kill them in a fashion that destroeyed the gene-seed)

and remember that nowadays a sorely diminished chapter needs decades to rebuilt their strength (see f.e. crimson fists, ultramarines or bloodangels, the latter needeing 650 years to rebuilt accoring to the novel  "space hulk")

sidenote: evben before the outbreak of the heresy, horus already planned for it and sent legions into trouble.