Ever notice that, after the fact, hugely successful companies have many "co-founders", while failed companies have only "early employees". VC's make it their business to know who the "real" founders of successful companies were (we try to be involved in their next company) -- and it's a small world, so not that hard to track this. Entrepreneurs hurt their credibility if they claim 'co-founder" status too generously. Conversely, having comported oneself admirably in a failed start-up is nothing to hide. So, tell the truth when you're pitching VC's.