User blog comment:Supahbadmarine/Too Many Loyalists!/@comment-1257337-20110604111635/@comment-10514705-20110606030153

I don't think I've ever come across that article before. I have seen the 60% (not 80%) of all chapters are founded from Ultramarine geneseed though. However it is still not concretely stated that the mixing of Geneseed occurs, and there are only 'rumours' and implications that other chapters may have mixed geneseed. Personally, as long as it only implied, mixing geneseeds is perfectly canonical and that it is only NCF when the mixing is emphasised (and) focused on as no canon chapter exists at all which reflects this. The trouble is this is a grey area that save for a few scattered examples is open to interpretation.