The article might have meant YC recouped their past investments in all startups combined:
"YC broke even on its past investments when Salesforce.com (CRM) bought YC company Heroku"
Since the sales price is above 200 million, YC's equity would be worth 12+ million, which likely surpassed the total monetary first-seed investments in every startup they did so far.
That is kinda staggering given that there are still many stars that are doing pretty well...that YC is yet to exit. From Dropbox to AirBnB to WePay to Wufoo to Justin.tv to Posterous to Scribd, etc. All of those I suspect, if they have an exit (I doubt Wufoo will - mainly because I don't think the founders are interested), it will be pretty substantial.
"YC broke even on its past investments when Salesforce.com (CRM) bought YC company Heroku"
Since the sales price is above 200 million, YC's equity would be worth 12+ million, which likely surpassed the total monetary first-seed investments in every startup they did so far.