Corporate action could be anything.... including name and ticker change, RS execution, increase AS needed for acquisitions. As we may guess, the OS needs to increase due to: CEO's majority position, private investors in UK and 5 acquisitions this year alone. The increased OS will likely be restricted for a period of time.
BTW I believe ZI has OS close to 400 million and trades at $52 PPS. Divide $20 billion MC by $52 PPS = approximately 400 million OS. Also check out their quarterly financials on Yahoo finance.
$CLHI
Disclaimer: This is in my opinion only, do your own dd.