Ah, I think you misunderstand the structure. They have structured the raise as two interrelated related funds. The two funds presumably invest in the same set of portfolio companies. I assume they structured it this way as way of reducing fees and perhaps because some LPs were interested in different levels of exposure.

  This is the same size as Andreessen Horowitz’s past two funds and, like each of those efforts,
  includes a primary pool (which can do both early and late-stage deals), plus an overflow pool
  for portfolio companies that require significantly more capital. 

  The breakdown this time is $1 billion for the main fund and $500 million for the parallel
  fund―the latter of which only collects management fees once capital is committed.

If this parallel fund had been able to invest in earlier funds (remember each fund is a separate company with a different set of LPs and GPs) I am sure they would have mentioned it.