Board Thread:Warhammer 40k General Discussion/@comment-4851119-20140118095944/@comment-24661246-20140415102144

I like to think that one of the two missing legions did not believe in the Imperial truth and were thus purged for this heresy. Possibly they had been corrupted by Chaos, that would help to explain how Russ seemed to be fairly knowlegdeable about it whereas the other primarchs were quite clueless.

The second legion was probably sent away by the Emperor or perhaps they saw the storm coming and made a break for it. Either way they are probably out there somewhere in the depths of space. With a fairly large empire of their own by now.