"Meaningless" is hyperbolic. How much would you pay for a share of Airbnb? More than nothing, I assume. I think one can conclude something from consummated, informed responses to this question.
Does 65B represent the actual money value that people will pay for the shares of 100% of the ~600 currently existing YC companies?
Does it tell us the average value? The mean? Standard deviation? Quintile distributions? P/E? Is that number just based on valuations from funding rounds? Projections?
It is literally meaningless. It is not verifiable. The standards that are used to calculate it are not explained. There is no explanation to how it relates to the companies in the portfolio.
I'm a bear by nature. I think that the current batch of SaaS unicorns have an unsustainable valuation, and I think this unverified number feeds into that.
What the returns will be is an unknown, of course. But to say that is "meaningless" is either naive or a misuse of the word. Stock prices and market caps are decided the same way.
Private stock prices are the last price someone was willing to buy that stock at.
It is slightly less simple, because you may give a discount for advice, but private stock prices are definitely reliant upon supply and demand. If one investor wants to set your valuation at $1B and another at $100m, you go with the one who offered a $1B valuation. There is occasionally a discount for advice/connections, but the mechanism that the highest bidder wins is generally the same. Private market stocks are by no means exempt from economics or supply and demand.
Total: $45 Billion.
Source: http://graphics.wsj.com/billion-dollar-club/
So they value the rest of the portfolio at $20 billion. Does that seem reasonable?
$65 billion / (940 companies) = $69 million / company