Visa's corporate website http://corporate.visa.com/about-visa/technology/transaction-... suggests that the quoted numbers, "40M of the 200M+", numbers are wrong or misleading. Possibly they are based on the highest volume day?

"VisaNet authorizes, clears and settles an average of 150 million transactions per day in 200 countries and territories."

Either way, the best way to prove an assertion based on numbers is to source it.