Proof for what? Smaller number of available women? That's obvious. That if larger companies hire the best of them, the remaining supply/quality will shrink? That's obvious too.
It sounds like they kept meetings deliberately off-the-record, but then again here on https://www.google.com/diversity/index.html there's stuff like "we’re committed to making our workforce more reflective of the world we live in". Number goals are unlikely to be published for obvious liability reasons.
