Board Thread:Warhammer 40k General Discussion/@comment-71.91.63.134-20150920063835/@comment-8881468-20150930180549

[quote] Though it is possible he could have sent a legion to combat them but it would have been the survivors of the 2 lost legions after their primarchs were removed for cause as the Emperor wouldn't have wiped them from all records otherwise.[/quote]

Doubtful, as Nids would have had the Marine genetic material prior to M40 and knowledge of the species would have been spread to all other legions and the Mechanicum