What do you mean by 25k+ banks? There were 25,000 different banks that owned Mastercard? Or is a 25k+ bank a particular type of bank.. Not come across that term before.
"Prior to its initial public offering, MasterCard Worldwide was a cooperative owned by the 25,000+ financial institutions that issue its branded cards." [1]
[1] https://en.wikipedia.org/wiki/MasterCard