vanillabean
The policy is published on
the Centurion Lounge Access website. Quoted in relevant part below...
Soliciting other Card Members to bring your guests into our lounge is not permissible. Additional guests over the complimentary guest limit require the purchase of a day-pass as stated in our access policy.
Guest access is per Card Member, not per Card. Family or guests may not enter or remain in the lounge unless accompanied in the lounge by the Card Member. No more than two guests per day will receive admittance to the lounge at no additional charge.
So, in any event, you may only have two complimentary guests at a CL per day. For your back to back business meeting hypothetical, even if guests 1 and 2 leave after the meeting, guests 3 and 4 must pay the $50 per day access fee.